I would hire an attorney on this one. Most likely you will have claims against the forger for fraud and theft. Also, you should call the police as forgery and theft are crimes.
Now, whether you could get your car back from the new party depends on the circumstances and whether the new party was considered a bona fide purchaser. Although you have said that the new party was unaware, there are many rules regarding whether a buyer is in fact a bona fide purchaser. If he or she is a bona fide purchaser and meets all the legal standards for keeping the property than you will have a difficult if not impossible time getting the property back. If the new party is not a bona fide purchaser or otherwise knew or at least should have known the transaction was not legitimate then you may be able to retake possession of the car and title. Again, the process can be tricky and time consuming so I would enlist the help of a lawyer.
I agree with Mr. Mitchell-Phillips' response. When you speak with counsel you will want to talk with them about the concept of "bona fide purchaser for value" as, depending on the facts, it may be that the individual who purchased the car without knowledge of the wrong-doing are themselves insulated from liability to you.