MyYearbook, a teen-oriented social network from New Hope, Pennsylvania, said today that it acquired five Android applications as it moves into mobile. myYearbook says the acquisitions are key since one-third of the site’s visits now come from mobile devices up from about two percent a little over a year ago.

Three of the five apps it bought: Toss It, Tic Tac Toe and Minesweeper have at least 1 million installs, according to the Android Market. The other two: SpringDroid and Line of 4 have between 500,000 and 1 million installs, according to the Market.

On top of that, the company bought FlockEngine, which supports social features in games like leaderboards, matching players to find opponents along with chat and messaging. The company says two employees, Chris Hager of Austria-based FlockEngine and James O’Brien of UK-based SpringDroid, will join the company.

Given the younger demographic of the site and a projected boom in sales of free or near-free Android smartphones this year, it makes sense to focus on Google’s platform. iOS is likely to be less affordable for teens.

Like Facebook, myYearbook has aggressively built out a revenue stream from virtual currency. Called “Lunch Money,” visitors can pay for it to play games or can earn it by watching video advertising from start to finish.