What sort of anti-social behavior? Many people take it to mean simply not socializing as much or having difficulties with interaction but anti-social more referres to essentially acting with no regard to others and even being outwardly rude/unpleasant to people.

Also does he want to meet new people? does he want to meet girls? Does he live on his own or with you? First of all there is always the internet to potentially meet people but that can be hit and miss...I mean like there is free dating sites but no garantee anyone will find anyone they actually end up wanting to meet IRL....aside from that I don't know if there are any sort of hobby/social group type things(might be more common for younger people ) but if there was something with people that had to do with an intrest he had then it would be a way to meet other people interested in that.