I put down my signature on a vehicle loan along with my sisters...problem is, the car payment is late.?

Last year, I helped my sister get a loan for a car by putting my name on an application with hers. I ended up having to be the primary, while she was the co-signer. At this time she was living with me and my wife and was making her payments. Now fast forward until up about a week ago when we kicked her and her lazy boyfriend out of the house. Not too long after this I got a note in the mail from the bank that financed the car saying it was already a month overdue and that last months and this months was due at the same time now. My question is: what are my options? I don't know where they live now because they were upset that I was kicking them out and just left, so I can't go repo the car myself. Are there any websites I can go to to help minimize the damage, or am I pretty much just beat?