Omg I have the same concern about my currently 13 yr old. The only difference is that he does try to look for his friends but for some reason the friends seem to not want to hangout with him. It hurts because I see his text and noticed the friends make excuses for not being able to hangout with my son or they just don't reply to his texts. I feel hopeless and don't know what to do. These friends only look for him when they want to but when my son wants to they have no time. I don't know what to do.
Sounds like he has a pretty busy life. And 13 year old boys don't typically share with their moms what is going on in their personal life. He probably is fine. However, next time you go in for a parent conference ask his teachers about it. Some of them may have a good perspective.
I have the same concerned about my 13 yr old son. He is honor student, has good grade, play tennis, and in the boy's chorus. But only has a few friends. Does not answer his phone calls, or text, does not check his emails. I am really worried about him.
And there is always the chance that he spends his spare time in athletics and studying - while his peers don't. As long as he is pulling straight A's (or close to it) and involved in sports - I wouldn't worry. When he feels the need, he will probably start to waste his time. Until then be happy (and supportive).
One person you might consider consulting would be your son's teacher. Ask his teacher if he/she has any concerns about his social interaction and if so, what might be the issues and/or solutions. You might wish to question any other adult who has contact with your child re social interaction as a sports coach or Sunday School teacher or swimming instructor, etc. Hope this helps ....