<PAGE>

                                                                    Exhibit 4(a)

VOID AFTER 5:00PM, PHILADELPHIA, PA
TIME, ON OCTOBER 21, 2004

THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER THE SECURITIES LAWS OF ANY STATE.
THESE SECURITIES ARE SUBJECT TO RESTRICTIONS ON TRANSFERABILITY AND RESALE AND
MAY NOT BE TRANSFERRED OR RESOLD EXCEPT AS PERMITTED UNDER THE ACT AND THE
APPLICABLE STATE SECURITIES LAWS, PURSUANT TO REGISTRATION OR EXEMPTION
THEREFROM.  THE ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF COUNSEL IN
FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER TO THE EFFECT THAT ANY PROPOSED
TRANSFER OR RESALE IS IN COMPLIANCE WITH THE ACT AND ANY APPLICABLE STATE
SECURITIES LAWS.



                            THE NETPLEX GROUP, INC.

              Warrant for the Purchase of Shares of Common Stock
              --------------------------------------------------


No. PMG-001                                              Up to 250,000 Shares of
Date: October 21, 1999                             Common Stock, $.001 par value

  FOR VALUE RECEIVED, THE NETPLEX GROUP, INC., a New York corporation (the
"Company"), with its principal office at 1800 Robert Fulton Drive, Suite 250,
Reston, Virginia 20191, hereby certifies that Pennsylvania Merchant Group (the
"Holder") is entitled, subject to the provisions of this Warrant, to purchase
from the Company, at any time after the date hereof and continuing for a period
of five (5) years (the "Expiration Date"), up to the number of fully paid and
nonassessable shares of Common Stock of the Company set forth above, subject to
adjustment as hereinafter provided.

  The Holder may purchase such number of shares of Common Stock at a purchase
price per share (as appropriately adjusted pursuant to Section 6 hereof) of
$3.00 (the "Exercise Price"), subject to the limitations set forth in Section 1.
The term "Common Stock" shall mean the aforementioned Common Stock of the
Company, together with any other equity securities that may be issued by the
Company in addition thereto or in substitution therefor as provided herein.

  The number of shares of Common Stock to be received upon the exercise or
exchange of this Warrant and the price to be paid for a share of Common Stock
are subject to adjustment from time to time as hereinafter set forth.  The
shares of Common Stock deliverable upon such exercise or exchange, as adjusted
from time to time, are hereinafter sometimes referred to as "Warrant Shares."
<PAGE>

  Section 1.  Exercise of Warrant; Vesting; Cashless Exercise.
              -----------------------------------------------

  (a)  The vested portion of this Warrant may be exercised in whole or in part
on any business day on or before the Expiration Date by presentation and
surrender hereof to the Company at its principal office at the address set forth
in the initial paragraph hereof (or at such other address as the Company may
hereafter notify the Holder in writing) with the Purchase Form annexed hereto
duly executed and accompanied by proper payment of the Exercise Price in lawful
money of the United States of America in the form of a check, subject to
collection, for the number of Warrant Shares specified in the Purchase Form.  If
this Warrant should be exercised in part only, the Company shall, upon surrender
of this Warrant, execute and deliver a new Warrant evidencing the rights of the
Holder thereof to purchase the balance of the Warrant Shares purchasable
hereunder.  Upon receipt by the Company of this Warrant and such Purchase Form,
together with proper payment of the Exercise Price, at such office, the Holder
shall be deemed to be the holder of record of the Warrant Shares,
notwithstanding that the stock transfer books of the Company shall then be
closed or that certificates representing such Warrant Shares shall not then be
actually delivered to the Holder.  The Company shall pay any and all documentary
stamp or similar issue or transfer taxes payable in respect of the issue or
delivery of the Warrant Shares.

  (b)  Vesting.  The Holder shall have the right to purchase 175,000 shares of
       --------
the Common Stock represented by this Warrant as of the date hereof.  The Holder
shall have the right to purchase the remaining 75,000 shares of the Common Stock
on or after October 21, 2000, provided, however, that the Company has extended
that certain Agreement dated October 21, 1999, as amended December 22, 1999, by
and between the Company and Holder in accordance with the terms of that certain
Agreement.  If that certain Agreement has not been extended by the Company in
accordance with the terms of that Agreement, then the Holder shall not have any
rights to purchase the remaining 75,000 shares of the Common Stock represented
by this Warrant.

  (c)  Cashless Exercise.  In addition to the rights of the Holder under
       ------------------
paragraph (a) above, the Holder shall have the right to exercise this Warrant,
in whole or in part, in lieu of paying the Exercise Price in cash, by
instructing the Company to issue that number of Warrant Shares determined by
multiplying the number of Warrant Shares in respect of which this Warrant is
being exercised by a fraction, the numerator of which shall be the difference
between the Market Price (as defined in Section ) 6(e) below) per share of
Common Stock on the date of exercise and the Exercise Price, and the denominator
of which shall be such Market Price per share of Common Stock.


  Section 2.  Reservation of Shares.  The Company hereby agrees that at all
              ---------------------
times there shall be reserved for issuance and delivery upon exercise or
exchange of this Warrant all shares of its Common Stock or other shares of
capital stock of the Company from time to time issuable upon exercise or
exchange of this Warrant.  All such shares shall be duly authorized

                                       2
<PAGE>

and, when issued upon the exercise or exchange of the Warrant in accordance with
the terms hereof, shall be validly issued, fully paid and nonassessable, free
and clear of all liens, security interests, charges and other encumbrances or
restrictions on sale (other than any restrictions on sale pursuant to applicable
federal and state securities laws) and free and clear of all preemptive rights.

  Section 3.  Fractional Interest
              -------------------

  The Company will not issue a fractional share of Common Stock upon exercise or
exchange of this Warrant.  Instead, the Company will deliver its check for the
current market value of the fractional share.  The current market value of a
fraction of a share is determined as follows:  multiply the Market Price (as
defined in Section 6(g) below) of a full share by the fraction of a share and
round the result to the nearest cent.


  Section 4.  Assignment or Loss of Warrant.
              -----------------------------

  (a) Except as provided in Section 9, the Holder of this Warrant shall be
entitled, without obtaining the consent of the Company, to assign its interest
in this Warrant, or any of the Warrant Shares, in whole or in part to any bona
fide officer, director or partner of Holder, provided, however, that the
transferee, prior to any such transfer, agrees in writing, in form and substance
satisfactory to the Company, to be bound by the terms of this Agreement as if
originally a party hereto and provides the Company with an opinion of counsel in
such form reasonably acceptable to the Company and its counsel, that such
transfer would not be in violation of the Act or any applicable state securities
or blue sky laws. Subject to the provisions hereof and of Section 9, upon
surrender of this Warrant to the Company or at the office of its stock transfer
agent or warrant agent, with the Assignment Form annexed hereto duly executed
and funds sufficient to pay any transfer or other tax payable in respect
thereof, the Company shall, without charge, execute and deliver a new Warrant or
Warrants in the name of the assignee or assignees named in such instrument of
assignment and, if the Holder's entire interest is not being assigned, in the
name of the Holder, and this Warrant shall promptly be canceled.

  (b) Upon receipt of evidence satisfactory to the Company of the loss, theft,
destruction or mutilation of this Warrant, and (in the case of loss, theft or
destruction) of indemnification satisfactory to the Company, and upon surrender
and cancellation of this Warrant, if mutilated, the Company shall execute and
deliver a new Warrant of like tenor and date.

  Section 5.  Rights of the Holder.  The Holder shall not, by virtue hereof, be
              --------------------
entitled to any rights of a shareholder in the Company, either at law or equity,
and the rights of the Holder are limited to those set forth in this Warrant.
Nothing contained in this Warrant shall be construed as conferring upon the
Holder hereof the right to vote or to consent or to receive notice as a
shareholder of the Company on any matters or with respect to any rights
whatsoever as a shareholder of the Company.  No dividends or interest shall be
payable or accrued in respect of this Warrant or the interest represented hereby
or the Warrant Shares purchasable hereunder until, and only to the extent that,
this Warrant shall have been exercised or exchanged in accordance with its
terms.

                                       3
<PAGE>

  Section 6.  Adjustment of Exercise Price and Number of Shares.  The number and
              -------------------------------------------------
kind of securities purchasable upon the exercise or exchange of this Warrant and
the Exercise Price shall be subject to adjustment from time to time upon the
occurrence of certain events, as follows:

  (a) Adjustment for Change in Capital Stock.  If at any time after October 21,
      --------------------------------------
1999, , the Company:

      (A)  pays a dividend or makes a distribution on its Common Stock, in
           either case in shares of its Common Stock;

      (B)  subdivides its outstanding shares of Common Stock into a greater
           number of shares;

      (C)  combines its outstanding shares of Common Stock into a smaller number
           of shares; or

      (D)  makes a distribution on its Common Stock in shares of its capital
           stock other than Common Stock;

then the Exercise Price in effect immediately prior to such action shall be
adjusted so that the Holder may receive, upon exercise or exchange of this
Warrant and payment of the same aggregate consideration, the number of shares of
capital stock of the Company which the Holder would have owned immediately
following such action if the Holder had exercised or exchanged the Warrant
immediately prior to such action.

  The adjustment shall become effective immediately after the record date in the
case of a dividend or distribution and immediately after the effective date in
the case of a subdivision, combination or reclassification.

  (b)  Adjustment for Other Distributions.  If at any time after the date
       ----------------------------------
hereof, the Company distributes to all of its Common Stock holders any of its
assets, equity securities or debt securities, the Holder shall be entitled,
without additional consideration, to the same distribution as it would have
received if it had been a holder of the Warrant Shares.

  This subsection does not apply to cash dividends or cash distributions paid
out of consolidated current or retained earnings as shown on the books of the
Company and paid in the ordinary course of business.

  (c)  Deferral of Issuance or Payment.  In any case in which an event covered
       -------------------------------
by this Section 6 shall require that an adjustment in the Exercise Price be made
effective as of a record date, the Company may elect to defer until the actual
occurrence of such event (i) issuing to the Holder, if this Warrant is exercised
after such record date, the shares of Common Stock and other capital stock of
the Company, if any, issuable upon such exercise over and above the shares of
Common Stock or other capital stock of the Company, if any, issuable upon such
exercise on the basis of the Exercise Price in effect prior to such adjustment,
and (ii) paying to the Holder by check any amount in lieu of the issuance of
fractional shares pursuant to Section 3.

                                       4
<PAGE>

  (d)  When No Adjustment Required.  No adjustment need be made for a change in
       ---------------------------
the par value of the Common Stock.

  (e)  Market Price.  The "Market Price" per share of Common Stock is the last
       ------------
reported sales price of the Common Stock as reported by NASDAQ, or the primary
national securities exchange on which the Common Stock is then quoted; provided,
however, that if quotes for the Common Stock are not reported by NASDAQ and the
Common Stock is neither traded on the NASDAQ National Market, on a national
securities exchange, on the NASDAQ Small Cap Market nor on the OTC Electronic
Bulletin Board, the price referred to above shall be the price reflected in the
over-the-counter market as reported by the National Quotation Bureau, Inc. or
any organization performing a similar function, and provided, further, that if
the Common Stock is not then publicly traded, the Market Price shall equal the
Conversion Price.

  (f)  No Adjustment Upon Exercise of Warrants.  No adjustments shall be made
       ---------------------------------------
under any Section herein in connection with the issuance of Warrant Shares
upon exercise or exchange of the Warrants.

  (g)  Common Stock Defined.  Whenever reference is made in Section 6(a) to the
       --------------------
issue of shares of Common Stock, the term "Common Stock" shall include any
equity securities of any class of the Company hereinafter authorized which shall
not be limited to a fixed sum or percentage in respect of the right of the
thereof to participate in dividends or distributions of assets upon the
voluntary or involuntary liquidation, dissolution or winding up of the Company.
Subject to the provisions of Section 8 hereof, however, shares issuable upon
exercise or exchange hereof shall include only shares of the class designated as
Common Stock of the Company as of the date hereof or shares of any class or
classes resulting from any reclassification or reclassifications thereof or as a
result of any corporate reorganization as provided for in Section 8 hereof.

  Section 7.  Officers' Certificate.  Whenever the Exercise Price shall be
              ---------------------
adjusted as required by the provisions of Section 6, the Company shall forthwith
file in the custody of its secretary or an assistant secretary at its principal
office an officers' certificate showing the adjusted Exercise Price determined
as herein provided, setting forth in reasonable detail the facts requiring such
adjustment and the manner of computing such adjustment.  Each such officers'
certificate shall be signed by the chairman, president or chief financial
officer of the Company and by the secretary or any assistant secretary of the
Company.  Each such officers' certificate shall be made available at all
reasonable times for inspection by the Holder or any holder of a Warrant
executed and delivered pursuant to Section 4 hereof.

  Section 8.  Reclassification, Reorganization, Consolidation or Merger.  In the
              ---------------------------------------------------------
event of any reclassification, capital reorganization or other change of
outstanding shares of Common Stock of the Company (other than a subdivision or
combination of the outstanding Common Stock and other than a change in the par
value of the Common Stock) or in the event of any consolidation or merger of the
Company with or into another corporation (other than a merger in which merger
the Company is the continuing corporation and that does not result in any
reclassification, capital reorganization or other change of outstanding shares
of Common Stock of the class issuable upon exercise or exchange of this Warrant)
or in the event of any sale, lease, transfer or conveyance to another
corporation of the property and assets of the Company as an entirety or
substantially as an entirety, the Company shall use its best efforts to cause
effective

                                       5
<PAGE>

provisions to be made so that the Holder shall have the right thereafter, by
exercising this Warrant, to purchase the kind and amount of shares of stock and
other securities and property (including cash) receivable upon such
reclassification, capital reorganization and other change, consolidation,
merger, sale or conveyance by a holder of the number of shares of Common Stock
that would have been received upon exercise or exchange of this Warrant
immediately prior to such reclassification, capital reorganization, change,
consolidation, merger, sale or conveyance. Any such provision shall include
provisions for adjustments in respect of such shares of stock and other
securities and property that shall be as nearly equivalent as may be practicable
to the adjustments provided for in this Warrant. The foregoing provisions of
this Section 8 shall similarly apply to successive reclassifications, capital
reorganizations and changes of shares of Common Stock and to successive
consolidations, mergers, sales or conveyances.

  Section 9.  Transfer to Comply with the Securities Act of 1933; Registration
              ----------------------------------------------------------------
Rights.
------

  9.1  No sale, transfer, assignment, hypothecation or other disposition of this
Warrant or of the Warrant Shares shall be made unless any such transfer,
assignment or other disposition will comply with the rules and statutes
administered by the Securities and Exchange Commission and (i) a Registration
Statement under the Act including such Shares is currently in effect, or (ii) in
the written opinion of counsel, which counsel and which opinion shall be
reasonably satisfactory to the Company, a current registration Statement is not
required for such disposition of the shares.  Each stock certificate
representing Warrant Shares issued upon exercise or exchange of this Warrant
shall bear a legend in substantially the following form (unless, in the opinion
of counsel, which counsel and which opinion shall be reasonably satisfactory to
the Company, such legend is not required):

     "THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
     SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER THE
     SECURITIES LAWS OF ANY STATE.  THESE SECURITIES ARE SUBJECT TO
     RESTRICTIONS ON TRANSFERABILITY AND RESALE AND MAY NOT BE TRANSFERRED
     OR RESOLD EXCEPT AS PERMITTED UNDER THE ACT AND THE APPLICABLE STATE
     SECURITIES LAWS, PURSUANT TO REGISTRATION OR EXEMPTION THEREFROM.  THE
     ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF COUNSEL IN FORM
     AND SUBSTANCE SATISFACTORY TO THE ISSUER TO THE EFFECT THAT ANY
     PROPOSED TRANSFER OR RESALE IS IN COMPLIANCE WITH THE ACT AND ANY
     APPLICABLE STATE SECURITIES LAWS."

  9.2  The Company agrees that during the term of this Warrant, the Holder shall
have the right to require the Company to register the Warrant Shares with any
subsequent registration statement filed by the Company.

  Section 10.  Modification and Waiver.  Except as otherwise provided herein,
               -----------------------
any term of this Warrant may be amended, and the observance of any term of this
Warrant may be waived (either generally or in a particular instance, either
retroactively or prospectively, and either for a specified period of time or
indefinitely), with the written consent of the Company and

                                       6
<PAGE>

the Holder of this Warrant. Any amendment or waiver effected in accordance with
this section shall be binding upon each future Holder of this Warrant and the
Company.

  Section 11.  Notices.  All notices and other communications required or
               -------
permitted hereunder shall be in writing and shall be deemed effectively given
upon personal delivery, on the first business day following mailing by overnight
courier, or on the fifth day following mailing by registered or certified mail,
return receipt requested, postage prepaid, addressed to the Company at the
address indicated therefor in the first paragraph of this Warrant and the Holder
at its address as shown on the books of the Company; provided, however, that
presentation of a Purchase Form and payment of any Exercise Price shall be
effective only upon receipt by the Company.

  Section 12.  Descriptive Headings and Governing Law.  The titles of the
               --------------------------------------
paragraphs and subparagraphs of this Warrant are for convenience of reference
only and are not to be considered in construing this Warrant.  This Warrant
shall be governed by and construed under the laws of the Commonwealth of
Pennsylvania without regard to any otherwise applicable principles of conflicts
of laws.

  Section 13.  Entire Agreement.  This Warrant and the other documents delivered
               ----------------
pursuant hereto constitute the full and entire understanding and agreement among
the parties with regard to the subjects hereof and no party shall be liable or
bound to any other party in any manner by any representations, warranties,
covenants or agreements except as specifically set forth herein or therein.
Nothing in this Warrant, express or implied, is intended to confer upon any
party, other than the parties hereto and their respective successors and
assigns, any rights, remedies, obligations, or liabilities under or by reason of
this Warrant, except as expressly provided herein.

  Section 14.  Severability.  In the event that any provision of this Warrant
               ------------
shall be invalid, illegal or unenforceable, it shall, to the extent practicable,
be modified so as to make it valid, legal and enforceable and to retain as
nearly as practicable the intent of the parties, and the validity, legality, and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.  To the extent permitted by law, the parties hereto waive the
benefit of any provision of law that renders any provision of this Warrant
invalid or unenforceable in any respect.

  Section 15.  No Waiver.  No waiver by any party to this Warrant of any one or
               ---------
more defaults by any other party or parties in the performance of any of the
provisions hereof shall operate or be construed as a waiver of any future
default or defaults, whether of a like or different nature.  Except as expressly
provided herein, no failure or delay on the part of any party in exercising any
right, power or remedy hereunder shall operate as a waiver thereof, nor shall
any single or partial exercise of any such right, power or remedy preclude any
other or further exercise thereof or the exercise of any other right, power or
remedy.

                                       7
<PAGE>

  IN WITNESS WHEREOF, the Company has duly caused this Warrant to be signed by
its duly authorized officer and to be dated as of this 21st day of October,
1999.

                                   THE NETPLEX GROUP, INC.



                                   By:
                                        -------------------------------------
                                        Gene F. Zaino
                                        Chairman and Chief Executive Officer

                                       8
<PAGE>

                                 PURCHASE FORM
                                 -------------


                                                      Dated
                                                            --------------, ----

  The undersigned hereby irrevocably elects to exercise the within Warrant to
purchase ______ shares of Common Stock and hereby makes payment of _____________
in payment of the exercise price thereof.



                                    Signature:
                                               -----------------------------
                                    Name:
                                          ----------------------------------
                                    Title:
                                           ---------------------------------

Name of Holder:
                --------------------------------
Address:
         ---------------------------------------

         ---------------------------------------

Taxpayer ID#:
              ----------------------------------

                                       9
<PAGE>

                                ASSIGNMENT FORM
                                ---------------


                                                       Dated
                                                            --------------, ----


  FOR VALUE RECEIVED, ____________________ hereby sells, assigns and transfers
unto _____________________________(the "Assignee"),  Taxpayer ID#_______________
  (please type or print in block letters)

 -------------------------------------------------------------------------------
                               (insert address)

its right to purchase up to ________ shares of Common Stock represented by this
Warrant and does hereby irrevocably constitute and appoint
_______________________________ Attorney, to transfer the same on the books of
the Company, with full power of substitution in the premises.



                                    Signature
                                              ---------------------------
                                    Name:
                                          -------------------------------
                                    Title:
                                           ------------------------------

Name of Holder:
                --------------------------------
Address:
         ---------------------------------------

         ---------------------------------------

Taxpayer ID#:
              ----------------------------------

                                       10