Provide your son with an opportunity to talk to you about anything and everything that's on his mind. Name his pain by telling him that you are sure that he must be devastated about his classmate's suicide. He may feel responsible in some way for his friend's death. Talk to him about those feelings and how even our closest family members can hide their darkest fears from us. Ask him what he might want to do to commemorate his friend's life, individually or with other mutual friends. It's important that life just doesn't quickly get back to normal with no time spent grieving. Ask the school how they plan to help the students cope with this loss.
Stay in closer contact with your son than usual. Let him know that he can share anything with you, without fear of losing your love. Look for whether he withdraws from what he normally takes pleasure in, including the company of friends and family. If he withdraws and behaves unlike himself for longer than two weeks, I'd consider some counseling. One cannot minimize the impact of the death of a teenage friend, especially one who has committed suicide. I know that you'll give your son what he needs.
