I've noticed a few forum posts asking about social media and content sites like Wattpad. I can honestly say that they can be wonderful not just for marketing, but also as motivation for that first draft. I talked about that for the Huffington Post not long ago: http://www.huffingtonpost.com/cynthia-dagnalmyron/how-wattpad-saved-my-writ_b_5269418.html
I have over 12,000 read on Wattpad http://www.wattpad.com/user/CynthiaDagnal-Myron for my first draft of Educational Experience, which is a pittance for Wattpad. But it has been very exciting for me. Seeing the read count rise after posting each chapter has been a thrill. It also helps me write with even more purpose, when I know there's an audience waiting. It's easy to find dedicated fans who let you know how you're doing right away, too! And with Margaret Atwood and others there cheering you on, it's just a lovely way to stay motivated. I've tried other sites, but Wattpad remains my favorite.
Having built followings on Twitter and Facebook before I began announcing my own writing gave me another audience, and that also helped me find lots of readers. People "tune in" for tips and quirky tweets, and then decide to check out my writing as well. I can get over 200 reads in a weekend after an announcement goes out. I never tweet announcements more than three days in a row, and they're scheduled strategically.
To help me with that schedule and to keep social media from eating up all of my writing time, I use Hootsuite, Tweetdeck and/or Add This. These tools let you schedule blurbs about your book--preferably a quote and link, not a "buy this book" message--thoughout the day. But as I said, I started by offering fun stuff that had nothing to do with my writing first. Now, I even have a few celebrity followers, and lots of agents and editors who see new chapters regularly. I love getting a direct message from someone famous--makes my day!
BTW: be sure to keep hashtag lists like #MSWL (Manuscript Wish List) on Twitter. #MSWL gives you a long list of the types of books publishers and agents are looking for. There are lots more, as you'll see as soon as you start that list. Agents and publishers will announce query days and more via those lists, so they're very valuable.
I haven't experimented with Tumblr or Pinterest yet, and Instragram is too much work for me. But I'm sure I'll dive in while I'm resting from that first draft, so that I can use them when it's time to market EE.
Hope this little introduction is of some use to some of you who haven't tried social media yet! I'm no expert, but I have had lots of fun getting acquainted with this brave but not so new world.