Alanon is for the families of addicts, whereas AA would mainly be for the addict themselves - although both have open meetings for anyone to attend.
I'g agree with others though that it's very important to understand that you cannot stop your son from abusing and/or force him to get help. You can support him of course...but he has to make the decision to quit himself. That's why it's certainly encouraging news to hear that he he wants to get help.