First, lets get a few definitions down before we go any further. Libel is written lies about you. Slander is spoken lies about you. The fact that videos are posted on Youtube would more than likely represent slander. However, the problem you have is that you mention that the photos taken of you came from MySpace. My understanding is that MySpace is not a fully secure site and if anything is posted on it, it could be subject to hackers or others who take things from it and post them elsewhere, which is what happened to you.
I believe you can flag Youtube and they will eliminate the pictures. If they don't take them down once you advise them that they are illegal or obscene, then they may potentially be held responsible for any damages that flow from their continued posting. That becomes a civil matter rather than a criminal matter in my view. I don't believe that youtube, which is available to everyone to post on openly, is responsible for something going up on it - even if they fail to take it down. At least not criminally responsible. Civil liability is likely, but that takes retaining an attorney who will champion your case for you. That's the route I would suggest and leave the criminal prosecution to those who are breaking penal laws.
A roundup of the best tips and legal advice.