Social networking development team.

[Myke]

... I disagree, i direct your attention to this thread. Notice people saying they use facebook. Although i think maybe some more research is needed.

Making that topic doesn't prove that there's a high amount of gamers on said social sites.
It just proves that people who are already here and already have SA use facebook and what-not. I'm not saying this is destined not to work, in fact, there maybe quite alot of gamers on those social network.
That said, you have to remember one thing; advertising on sites could bring bad publicity along with good publicity.

An example being a WWII server that was being developed months back.
One of the developers/players on it made a video on youtube highlighting the features of it. That video alone brought a botnet attack on GTANet (or so i heard).

I'm not telling you not to do it, by all means go for it. Just be ready to face the consequences if the worst case scenario happens to come out of it.