A loyalty scheme run by start-up Plink will give Facebook Credits to consumers in return for purchases at Taco Bell, Dunkin’ Donuts and others.

This aims to take advantage of the boom in virtual currency, which is currently a $2.1bn industry.

After registering a credit card with Plink, users are rewarded with Facebook Credits each time they make a purchase in participating stores – Plink then takes a percentage of each sale.

Customers can use the virtual credits to buy additional content while playing games like FarmVille and The Sims.

So far US brands Taco Bell, 7-Eleven, Dunkin’ Donuts, Quiznos and Red Robin have signed up for the loyalty scheme, so the focus appears to be on fast food outlets for the moment.

Plink will target Facebook ads at users who have ‘liked’ the brands on the social network, and will also promote the scheme through ads in Facebook games.

This is a low-cost method of rewarding customers for their loyalty, as there are few overheads involved in topping up someone’s account with credits.

Not only is it a cost-effective way of driving footfall, the scheme also taps into a market that is predicted to grow to $4.8bn by 2016.

It’s not just Facebook that is reaping the benefits of the freemium games model though – over half of the top grossing apps in both Apple’s App Store and Google’s Android Market use this model.

You can read the experts’ view on how brands can make money and promote their brand using the popularity of virtual currency here.