Visit the U.S. Embassy or Consulate location nearest you in China. Bring with you any form of identification you already have -- unless your belongings were stolen and you have none.
Explain your situation to an embassy employee, and begin the process of obtaining a new visa. You must fill out forms, provide contact information for any American friends or relatives that can vouch for your identity -- if your identification was lost or stolen along with your visa -- and you must pay any applicable fees.
Provide the embassy with all of the information they require to apply for a new visa. The U.S. Embassy will do everything in their power to issue a new visa to you as soon as possible, so that you may exit China and return to the U.S.
