How do I tell my son that he needs alcohol rehab?

My son, Matt, has been drinking since he was 16 and I would like him to be sober again. He's not talking to me about it because he would say that I am not always around. And he's also failing in school. I don't even know who his friends are. He needs help and I don't know how I can help him if he keeps pushing me away. Please tell me how I can convince him to get alcohol rehab.

: http://alcoholdrugstreatment.info/how-do-i-tell-my-son-that-he-needs-alcohol-rehab