Has your son been able to keep in touch with old friends? Writing letters or emails, phoning old friends, and going back to visit or inviting them to visit you can help with the adjustment.
Try to help your son find friends with similar interests in your new community. Joining a Boy Scout troop, a soccer team, a drama group, or some other group that interests your son can help him feel more comfortable. Even if the new friends he makes go to other schools, once he begins to connect socially he will feel better about things. Making friends at his school and in the neighborhood will be easier as well.
You can also invite children from your new neighborhood over to play, to go to a movie with you and your son, or to stay at your house for a sleepover. It may be hard for your son to make this first move, but once he gets to know the other kids on his own turf and they get to know him, becoming friends will be easier.
Talk with the school counselor. He or she may offer a small group for new kids in the school to help them get to know each other. The counselor may also be able to give your son some support at school during the day and help him connect with other kids with similar interests.