Facts: an internet version of "happy slapping" which has nothing of happy but the name, for it is simply to beat someone up and diffuse the filming by phone or by the internet, here it was via YouTube. Can't see how one can legally argue criminal liability of YouTube: the company obviously did not know about the action before it was committed and can't in any way shape or form "aid, abet, advice..." to committing assault. Hopefully people seem to see sense.
The only liability could be if YouTube did not remove the video once informed of it...
"Video of teen beating raises questions" (11 April 2008)