My 19 year old son needs help

My son is shutting himself off from everything at the moment. He has a part time job and also goes to college. He spends the rest of his time in his room. He is clearly unhappy. Possibly depressed. He is very down about is future. He is very hard to talk to. I try chatting to him in different ways but nothing helps. He avoids spending time with any family.  He doesn't have friends or anyone outside myself and his dad to speak to. We feel helpless as anything we try to do to help him doesn't help at all. Nothing seems to interest him. I don't know what to do and I am worried about him all the time. He seems to have no motivation to do anything and has anxiety to try. He's a lovely person and has so much potential but has a brick wall around him which is hard to get through to him or for him to climb over. I don't know what to do for him.