G.G.
As a mom and teacher, I definitely don't think he has a personality disorder. But I do agree it would be a good idea to encourage outside interests. As for encouraging friendships, how about asking him to invite a friend to join the family at home (for dinner and a game?) or on a night out (to mini golf or the arcade?). That way, you could act as an example and facilitator of your son's relationship with another kid his age ... that may be hard for him and may explain why he avoids those situations. Eventually, I think he would get more comfortable with the friends who routinely accompany the family and that may spread to relationships with other kids.
My daughter has no interest in others and would prefer computer and TV 24/7. When my husband and I go on date nights, we require her to have a friend over so she's not alone. That's what we tell her. The real reason is that we want her to spend time with other girls her age. Any little step will help toward the ultimate goal of having her not be lonely when she's grown.