I went through something similar with my then 14 year old daughter when I got remarried and move to a different school district.
I would recommend you contact the specific guidance counselor of the school that will be working with him and his new class schedule and find out how they orient brand new students. My daughter's school actually has a group of kids that volunteer to get paired up with new students to give them the school tour and sort of buddy with them so they can get acclimated. My daughter and the girl who was her "buddy" are still good friends to this day.
If your son is in sports or clubs at his current school, I would contact the team coach and get him enrolled ASAP, even if it is in the middle of the season. The sooner he meets kids with is same interests, the better.
I'm not sure how far away his old friends are but it has been really important to my daughter that I keep her in contact with our old neighborhood and those kids. It really amazes me how close she remains with that group of neighborhood kids. Just because they live 25 minutes away, we still plan stuff and have them over and she goes there for overnights. It's work but it helps soften the trauma of moving. Teens are really sensitive about their friends and their importance.
I would spend one-on-one time with him, give him a tour of the town, mall, restaurants, places you go a lot to make him feel like he is sort of familiar with your life. If there are neighborhood kids his age and you know the parents, see if you can get them together to meet. Teenage boys love video games, so that is always a common interest they could share to get to know one another.
I wish you lots of luck.