My 16 year old son is not social at all

I understand that my son is introverted, but I feel like he should be more social than he is. He NEVER does anything with friends outside of school. When he's at home he always goes to his room and closes the door to do homework. When we have dinner he comes down and takes a plate of food to his room, he never wants to eat with us. He never does anything with his friends on the weekends, he stays in his room and reads books, watches movies and listens to music. He's not interested in any of the sports at his school or any of the clubs. He has a girlfriend, but he met her through tender, so he didn't have to be social to meet her. Plus she's just like him so when she comes over they do not talk very much. She eats dinner with us sometimes and she doesn't talk very much at all. They usually hold hands at the table and share food. When she usually goes to his room and they cuddle and read books or watch movies. I think they spend more time kissing than talking. I just don't know what to do. I think that he needs to be social and have friends that he does things with. What should I do? via /r/Parenting http://ift.tt/2dws8KC