How can and you help your child make friends?

My son is 11 and in 5th grade and he just expressed to me today that he only has 1 friend at school (and he refers to him as a 'kinda sorta friend'), that's it. He says he has no one to sit with at lunch and at recess he just walks around by himself. He has only been going to this school for 3 months but I figured he would have made lots of friends by now! Im not sure if I should talk to his teacher or principal about my concerns or if I should just leave it alone and let kids be kids lonely or not??