Hmmmm that is tough. I don't think I would come right out and say I think you are depressed. But find some way to reach out to him and offer help. Maybe look for little opportunities to build up trust and pry just a little. You might be that one person in his life that notices and cares. He may remember you forever for that. How do you do it with a rebellious boy who deep inside wants someone to help him. That's hard. I was that boy. I think sharing your own experience in little bits is a good way to build trust.