Hello hopeless85, welcome to Psych Central.

As he is classed as an adult now, I don't think you can force him to seek help unless he is a danger to himself or others. You can talk to him about your concerns and tell him how scared you are for his health but unless he is willing to seek help himself, you are in a difficult position. You could try having a word with his doctor but I'm not sure they are able to do anything unless he is suicidal or a danger in some way. You could try contacting your local mental health charity to see if they have any ideas, different places in the world have different systems so they might be able to give you different advice.