Just anecdotally from my reviews of police reports it appears that chatrooms are the hunting grounds of choice and while there may be chatrooms connected with these social networking sites that the sites themselves are really secondary to the chat. I have found it more and more useful to review an opposing witness's "pages" on these sites. I find them most often useful in divorce cases but interestingly even in a recent homicide case the "victim" turns out to have some interesting postings.
Over the past few years there has been a huge number of grandstanding politicians claiming that social networks like Facebook and MySpace were breeding grounds for online predators. . .. Of course, it turns out that the entire premise is faulty. A few years back we pointed to a study that showed the problem was entirely exaggerated. . . . Now there's a new study out going even deeper in noting that sexual predators are unlikely to pretend to be teenagers using social networks, but rather are very upfront about who they are and what they want. In most cases, the victims knew that they were chatting with an older person, and believed that they were in a legitimate relationship, rather than being tricked. Once again, this suggests that all the hype and new laws being proposed to deal with the "problem" of predators on social networks are misplaced.
I remain agnostic on the issue.