Can you sue someone for stealing your pictures from MySpace/Facebook and using them as their own?

You can try, but aren't likely to get anywhere. You put your picture out there with public access so should expect possible theft of pictures. Now, if they are saying they are you, doing things that result in diminishing you in some way that can effect your real actual life (like getting word out to your community that you like to look at child etc.) Other then that a judge won't want to waste their time.