goto
www.imchaos.com
create a link spy
set it up in your profile with something that says, "check out these crazy pics from last friday's party" or some stupid shit. just something that will get their attention. When they click on it, it'll track who clicked it and will give an IP address and a map to whomever the potential culprit is. if you can match up the fake screen name with a real one you know who it is.