Myspace used to be a great resource, when their classifieds weren't screwed up. It seems Myspace is fast becoming a relic of days past, however.
I've gotten quite a few jobs (I am a songwriter/ghostwriter) via this forum. Keep an eye on the Collaborations section and this section, a songwriter pops up every few weeks/months advertising their services.
If you're in need of a songwriter at the moment, e-mail me at ET@FreelanceLyrics.com , I'd be interested in hearing the details of the project(s).
attend shows! Thats how I got started.... not with hip hop but when I was doing my thing with the guitar... You meet some great people and it helps huge to collab with other writers...