I've been successfully using that 123people.com website that Paul Mitchell recommended to *stalk* hard-to-find
But I just found another website that combs the social networking sites a little better and I've already used it to locate a couple of lost
It's most aptly named - KGBPeople.com.
Of course, the first thing you should do is search for yourself and see how visible you are. I believe you can actually use this site as well to manage your own public profile.
See also - Tales of FaceBook Stalking.