Contact everyone you know. You may be surprised by the people they know. Make yourself pick up the phone and call. I it helps to assign yourself a quota of calls to be made each day. The more phone calls you make the easier it will become.
Email is a perfectly acceptable way to network as well.
Keep your message brief and to the point and be to sure to check your spelling, grammar and punctuation. Formal networking works too - try going to a business social or an association meeting or event. You'll find that many of the participants have the same goals you do and will be glad to exchange business cards. If you're shy, volunteer to work at the registration table where you can greet people as they come in or bring a friend to walk around the room with you - there's security in numbers. As well as networking the old fashioned way, use the internet to network.