In fact, you may be better off reserving the credit card for emergencies and paying cash for most purchases. While it's against the law for the Thai vendor to pass the fee that the credit card company charges them on to the customer(approximately 2.25% to 3.5%, depending upon card type), it's quite common for them to do so, and it's usually not negotiable -- you either pay the surcharge or don't use your credit card. They may even attempt to charge 4 or 5% instead of the 2.25% to 3.5%.
For lost cards:
Master Card: (662) 256 7326-7
Visa: (662) 256 7326-7
American Express: (662) 273 5100 or (662) 273 0022
Diners Club: (662) 238 2920 or (662) 238 2680
Major credit cards are accepted in most establishments and shopping centers, particularly the larger ones in Bangkok and the more touristy areas. However, there are occasionally additional fees placed on charges by both the retailer and your card provider.