Under the Fair Credit Billing Act (FCBA) the most you can be held liable for when your credit card has been stolen is $50. However, if you report the loss before your card has been used (or the fraudulent charges involve your credit number and not the card itself) under the FCBA you are not liable at all and do not have to pay the card issuer any money. But if a thief uses your card before you are able to report it missing, the most you will be liable for is $50.
It is a good idea to watch your billing statements carefully in the months after your credit card goes missing. If any charges appear that you did not make, be sure to contact the card issuer immediately.