Most likely he is with the drug dealer. If you have any inkling as to where he gets his drugs from maybe have the cops look there for your car. Have the cops search hotel parkinglots for your car. DO you live in a small town maybe? ANd Id be careful of telling his buddies at NA meeting that you reported your car stolen. They may very well tell him and he will just trash and ditch the car to get back at you. So try to keep this between you, your family, his mom that he stole from, and the cops. I think he'd never imagine that you'd report the car as stolen so he may be careless. And if you find the car before thecops do, PLEASE call the cops to let them arrest him. He needs to pay for his actions. Whats Grand theft to an addict? Do not let him in or come face to face with him from this point. For your own safety. He stole your car whos to say what he may do next. But just understand its just a car. A least its covered by insurance. At least this may be the final straw for you. The faster you get him out of your life the less you have to deal with this. Its just stuff but at least you are ok at least physically. You are at a stand point now where you get back on for another ride, or run the other way for some peace of mind.
I hope you get your car back one way or the other. I pray for your strength to keep moving away from the addict.