Short version: getting someone else to tell your story for you; incentivized word of mouth. Here's a few of the companies in the space directly and indirectly.

intellifluence.com -- mine
6ixagency.com
acorninfluence.com
adly.com
adretweet.com
amazingdealsgroup.com
amazingdealsnreviewsclub.com
amazingreviewsclub.com
amazonreviewernetwork.com
ambassadher.com
amzrc.com
amzreviewtrader.com
apexdrop.com
audigent.com
bazaarvoice.com
beafreelanceblogger.com
beatly.com
behance.net
bestsocialpr.com
bigfra.me
blanket.media
blogacious.com
blogdash.com
bloggerbridge.com
bloglovin.com
blogmint.com
blogprwire.com
boostinsider.com
brandbacker.com
brandnew.io
brandsnob.co
buzzandgo.com
buzzerati.com
buzzmg.com
buzzoole.com
buzzstream.com
bzzagent.com
cartcam.com
channelfactory.com
channelpages.com
cision.com/us/communication-cloud/
clearvoice.com/marketplace/
clevergirlscollective.com
contentblvd.com
contently.com
contentmarketer.io
contentmarketingstack.co
contidio.com
cooperatize.com
copromote.com
crowdcontent.com
crowdly.com
crowdtap.com
cycle.media
dealgogogo.com
DealsForReviews.com
delmondo.co
distroscale.com
dollardealreviews.com
dollarreviewclub.com
dotwriter.com
dynamicsignal.com
eleve.co
elitedealclub.com
evolvesinc.com
exomatch.com
exonia.net
experticity.com
exposely.com
extrahyperactivenetwork.com
famebit.com
fanbytes.co.uk
fango.me
fanwise.com
fashionprgirl.com
fbamarkets.com
fieldnation.com
findyourinfluence.com
flippersmack.com
fluvip.com
fromote.com
fullbottle.co
fullscreenmedia.co/creators
galoremag.com
getader.com
getambassador.com
getevangelized.com
getlittlebird.com
getreviewed.org
getshout.io
getswayd.com
getwordperks.com
giveawayservice.com
gnackapp.com
go.kred (empire.kred is the trading platform)
go.nuvi.com
grapevinelogic.com
grinapps.com
grouphigh.com
gushcloud.com
hashtagpaid.com
helium.com
hellosociety.com
hirefluence.com
hivency.com
honestfew.com
Hypetap.com
hyprbrands.com
ifluenz.com
imagency.com
Insense.pro
influence.co
influenceandco.com
influencepeople.com
influencer50.com
influencerdb.net
influencerconnect.com
influencers.club
influencersatwork.com
influencersg.com
influencive.com
influenster.com
influential.co
influgram.com
influicity.com
inhouse.team
innetwork.net
insightpool.com
instabrand.com
iplus.co
itrudeals.com
izea.com
jamballa.com
juliusworks.com
klear.com
klout.com
kontentcart.com
kudobuzz.com
lightningpages.com
linkfromblog.com
linqia.com
littlesway.com
loot-app.com
markerly.com
market.nmrkt.com
marketplace.matadoru.com
mavensocial.com
mavrck.co
media-part.com
mediakix.com
misfits.social
musefind.com
naritiv.com
neoreach.com
newlinenoosh.com
newscred.com
ngage.social
Niche.co
Nichify.com
octoly.com
onalytica.com
onmogul.com
outreachify.com
paidpertweet.com
patreon.com
paypercontent.net
peg.co
phlanx.com
pinchme.com
pixability.com
pond5.com
popularpays.com
powerreviews.com
Preen.Me
pro.iconosquare.com
promoto.co
productpilots.com
producttestinggroup.com
publicfast.com
rainmakercollective.com
reach-labs.com
reachbird.io
readypulse.com
reelio.com
revfluence.com
reviewclub.io
reviewkick.com
reviews4success.com
rewardstyle.com
rightrelevance.com
sampler.io
scripted.com
scrunch.com
seedingup.com
select.co
shespeaksinc.com
sideqik.com
smallgirlspr.com
smartviral.com
snagshout.com
Snapfluence.com
Social-Friendzy.com
sociabuzz.com
socialix.com
socialoholic.com
smiley.socialmedialink.com
socialrank.com
socialyte.co
sparkinfluence.net
speakr.com
splashscore.com
sponsokit.com
sponsoredmentions.com
sponsoredsocial.com
sponsoredtweets.com
sprinklr.com
stargazer.co
studio71.com
stylecoalition.com
swarmcontent.com
swayyem.com
swaygroup.com
swayops.com
tailify.com
takumi.com
tapinfluence.com
terakeet.com
terareach.com
theamplify.com
thecirqle.com
theexposure.co
themidgame.com
themobilemedialab.com
thepivotpeople.com
theshelf.com
thinkrenegade.com
thuzio.com
tid.al
tlistinc.com
tomoson.com
toprankmarketing.com
topreviewzone.com
totems.co
tourn.co
traackr.com
trendrz.com
Tribegroup.co
triberr.com
triond.com
tru-signal.com
tubularlabs.com
tvinkle.com
tweetangels.com
uberzonclub.com
unitedbloggers.no
unityinfluence.com
upfluence.com
uptweet.com
vaynermedia.com
vazoola.com
velocenetwork.com
vidfall.com
vidrocket.com
vipon.com
viralking.co
viralnation.com
vity.co
vizified.com
voltu.com
webfluential.com
webrand.com
weconnectsocial.com
weinfluence.co
whalar.com
whatsblog.com
wibber.io
withfluence.com
workew.com
writeraccess.com
xberts.com
yotpo.com
youtube.com/yt/creators/
zerys.com
zoomph.com
zuberance.com