Social media tools are wonderful all the time (especially because they're free), but they're even more wonderful when they're just starting out. You can make faster progress in the foothills of the audience mountain than you can at the peak. Take it from a digital PR professional: one of the easiest ways to make social media work for your brand, your book or your business, is: GET IN EARLY.
I benefitted from this once when fellow techies told me about Twitter in early 2008 and I joined it long before everyone and their brother, and as a result, I built a community of influential media contacts. I again benefitted from this strategy last night when I joined Ladies Who Critique. This excellent platform connects writers to one another for formal critiquing partnerships. (And guys, don't despair: There's plenty of menfolk on there, despite the moniker! UPDATE: I checked with the founder and she is happy for men to join. Come on down!)
I don't love every social media platform, in fact, the majority drive me nuts. But this site is easy to use: it has all the functionality you want, but not too much to get you bogged down.
Right now this community is small and I was able to find a potential match with just one message after about twenty minutes exploring member profiles. However, and I know this from experience, once these platforms become really popular, it becomes harder to rise above the noise.
So, get in now, get a critique partner, and "take your writing to the next level." (Their motto). Thank you to Laura Pepper Wu of 30 Day Books for creating this platform.