Co-Signer Took Car and Isnt making payments?

I got a co-signer on a car i bought in 2007 i left out of state for an emergency and when i returned the co signer had gotten a duplicate key from dealer and took the car. this was two years ago am I still accountable for the vehicle even though she took the vehicle? She can no longer make payments and now I have a warrant for my arrest for the money owed