We are unable to give you legal advice at this site. You should seek legal counsel to find out if the auto repair shop is liable for your car being stolen off of their lot. Also go through any paperwork you might have signed at the repair shop. Some auto garages will have you sign a document that has a 'hold harmless' clause that basically means they are not to be held responsible for any damages or if your car is stolen.

If you find that the repair shop is not legally liable and if you have comprehensive coverage on your vehicle you should contact your insurance company to place a claim.