Well.. to some extent. I'm usually on quite a few social networks, yet I don't socialize that well. Funny how that works.
I put some profile out and if people like it, they can hit me up. I rarely send out something by myself. I feel that, if I were to push myself up to someone, I do have some kind of "obligation" to be interesting, whereas, if someone contacts me, I have it less. I'm not saying that the other person should have this obligation though.
I used myspace back then and some dutch networks. Currently I'm on facebook and google+ (the latter, I have yet to figure out). I have msn, I just don't use it that much. I only have people I know in real life in there. And I have their phonenumbers as well. I recently got skype, but only as means to chat (type) with a friend of mine, who stopped using msn. As for facebook actually... most people in my list are folks I've ran into at some point. People I've been with in bands, people who I met at some kind of tournament, people I met at some club... and that actually is far below par for someone who, to some extent was a familiar face in this area. (being a heavily pierced vocalist in a local metalband helps, lol). I still have an account on Vampirefreaks, but that's more of a subculture social network. That, to me is good to get updates on music and all, but I rarely do real "networking" there.
I feel, that with all social networks, it dwindled down to "I'm old" in the sense that people who are more into this networking stuff are pretty much thinking "what the hell is he doing here?" or "he's 29, I can't befriend him as an 18 year old". And apparently people my age are all married, have children and are settled down.
So, do I use the internet to socialize? n......eah.... it's a decent platform to put yourself out and see if you can meet likeminded people, and even more if you're not in a big(-ish) city. I just barely initiate contacts myself. Even out of all my facebook friends, I added about 5 myself, and others "found" me.