most teens use the “networking” sites to hang out with the friends they already have.

While that is technically correct, it does imply that they *don’t* use it for other things like making new friends. The data however, says that almost half the users do exactly that. 49% is a huge number of people. I, for one, use Livejournal to do my “social networking”. At first, I didn’t know a lot of people, then very quickly, I became friends with several of them. I’ve actually reached a critical point where adding and making new friends would be too much, and I wouldn’t be able to keep up with them. I am not so sure the research delves into such possibilities. (It falls into both “making new friends, *and* keeping in touch with friends I already have and/or “rarely see in person’.

I don’t think people go into the social networking sites specifically looking for new friends without an existing infrastructure already using that site. New friends just kinda “happen” (friends of friends).