One important fact you have omitted: do you have possession of the car? If you do, then you have no grounds for a suit. You failed to perform "due diligence". You could have required your (ex)friend to show you the car payment documentation, but since you didn't, you assumed the risk that she wasn't being truthful. So, if you have possession of the car, keep it until it is repo'd. The bank will sell the car for a pittance and sue her for the shortfall. On the other hand, if she still has the car, you can sue her for unjust enrichment. If that is how you proceed, you will absolutely need her address, it would be impossible to proceed without it. There are ways to track someone down, or you can hire a "skip tracer" or private detective to do it for you.
Answered on Jan 23rd, 2013 at 10:44 AM