Need more Facebook Credits to support your virtual shopping habit? If you are in the United States, you’re in luck because PayNearMe is giving away up to 100 bonus Credits per user when you buy them in a 7-Eleven store.

The promotion, which started in the Seattle area last week and went nationwide on Monday, is offering Facebook users an extra 10% when they buy Credits using a PayNearMe slip. The first customer to a designated store will also receive a bonus 50 Credits.

PayNearMe is running the giveaway to promote its business, which lets the 27% of American households without a credit card buy goods and services online and pay in cash at a 7-Eleven store. It should also help boost the profile of Facebook Credits, complementing Facebook’s own efforts, such as its recent moves to give away Credits to selected users to show them how it works and encourage them to try it out.

Since Facebook announced the virtual gift store would close this month, games and a few other applications are the only place to spend Credits. The social networking site, which gets a 30% cut when users spend Credits in games, hopes the common currency will drive the growth of micro-transactions for virtual goods within games. Prior to the introduction of Facebook Credits, users had to complete separate transactions with every individual game developer.

To be in the running for free Credits, users must connect through Facebook, enter their zip code, print the slip and then go to a 7-Eleven store. PayNearMe has this video to explain how it works: