Domino’s credits Facebook and Foursquare promotions for lifting online sales by 61 percent in the U.K. and Ireland during the first half of this year compared to the same period in 2009. The international pizza chain also announced on Monday that web-based sales now account for 33 percent of its revenue, compared to 26 percent in 2009.

“Anything that helps to drive people to our online ordering page is always going to help drive sales,” said Georgina Wald, spokesperson for the London-based division. “So when we use social media, we make sure there are plenty of ways to quickly get to the ordering site.”

Domino’s leverages a corporate Facebook page with 37,000 fans/”People Like This” for national campaigns. Similar to user rewards programs like Foursquare’s mayor system and Yelp’s dukes and duchesses, the pizza brand has an ongoing “Superfan” promotion. The male and female who bring the most friends to the Facebook page are anointed “King” and “Queen,” respectively, for the week and rewarded with a free pizza.

The company also encourages its 627 stores to set up Facebook pages for local marketing purposes. Some U.K. locations – like in Plymouth and Huyton-with-Roby – have over 1,000 fans apiece. The Plymouth store ran the following promotion on its page during the World Cup last month:

“Buy any Pizza at regular price and we’ll give your boss a Free Pizza – butter them up to be allowed to watch the game!! This offer is available to all offices and workplaces from 11am – 4pm today! Just contact your local store!! COME ON ENGLAND!”

And Domino’s has gotten a quick return from Foursquare after implementing a program with the geo-location service in late May. “We’ve had nearly 10,000 check-ins since it launched from around 3,500 unique visitors,” Wald said.

For all locations, a Foursquare check-in garners a complimentary side dish when customers spend more than 10 British pounds. The aforementioned Huyton-with-Roby store created a YouTube video (see below) that explained how Foursquare generally works, as well as the location’s check-in reward – free garlic pizza bread.

The brand has also built up 531 followers on Twitter. As was the case with Facebook, some local stores have taken to Twitter. For example, a Lincoln, U.K. location has nearly 300 followers. It tweeted the following promotion yesterday: “Thank pizza it’s Tuesday! Don’t forget it’s Two for Tuesday today – buy one medium or large Domino’s #pizza and get another one free.”

Outside of social media, Wald said search marketing has been another area of emphasis in recent months and has contributed to the increased online sales. “In addition, we have used tools such as [an] affiliates widget to encourage people to put their own link to the online ordering site on their blogs and Facebook pages,” she said.

Follow Christopher Heine on Twitter at @ChrisClickZ.