You need to take him into your local county A&D program, while he is still 17, and get an alcohol and drug assessment completed. I know it won't be the most popular decision, but if you don't show that you are the one in charge, and nip this in the bud, it will only get worse. Bring him back home, if he runs, then the law, and or social services will get involved, which will be a good thing as they can force him into treatment. You can't let him dictate where he is going to live, and what he is going to do, otherwise, you will become his emotional hostage.
We don't have a local county A&D program and I don't have money to take to a place like that.