Hi, I'm Scott!
I'll try and provide some perspective on this issue that I hope you find helpful.
Be aware I am licensed in California only, and in any case, lawyers here cannot provide legal advice to specific legal problem, rather we can only address legal issues generally.
That said, call back the police and insist that you want to file a criminal complaint.
That is your perogative. Their perogative is not investigating the complaint, but there's not much you can do about that.
Nevertheless, filing a criminal complaint will be another bit for the civil action against the person for, at worst, larceny, and at least conversion.
You might try self-help first: calling the person and asking him to return the car so that the situation doesn't escalate.
Probably, you can also hire a "repo man" as self-help to get it back (this is called 're-capture of chattels'), but be sure you do have legal title and that there is no orther or superseeding claim on the vehicle -- because if there is, YOU would be liable.
In all likeihood, this is going to take a while if you have to go by legal mechaisms, and some expense in terms of filing fees and lawyer fees, so be prepared.
I hope this provided some perspective you found useful -- if so, I would appreciate a positive rating.
Thanks & Good Luck!