what to do if you have the "lost" car

Is the guy cool about it or an ***? If he's cool about it, think about what you would sell the car for. Offer it to him for that. Make sure it's a price that you are comfortable with. Put yourself in his place. How badly would you want it back? While you might really like the car, to him it may represent something much more. I'm not saying you should do it, but consider every angle. It would be really nice of you. We only go around once.