If people have stolen your video and re-uploaded it to Youtube, you can ask Youtube to remove it. I have done this in the past and it worked.
See [URLnf="http://newmediarockstars.com/2012/11/4-steps-you-should-take-if-someone-is-stealing-your-youtube-videos/"]here[/URLnf] an interesting article and info on how to do this.