Japanese games developer DeNA is to acquire San Francisco-based ngmoco – a maker of iOS games – in a deal they claim will create “the world’s largest mobile social games platform company.” The main goal of the tie-up is to create a smartphone version of DeNA’s social games network, Mobage, and launch it outside of Japan. According to ngmoco, Mobage has “tens of millions of users in Japan who play many hundreds of applications all woven together through a connected service.” ngmoco said it will now “lead DeNA’s efforts in the Western world.”

In a joint statement, the two companies said they would develop “a unified open developer platform that combines ngmoco’s state of the art smartphone technology framework with DeNA’s pioneering Mobage Open SDK.” The platform is designed to help developers target iOS and Android smartphone users in both Japan and the West.

ngmoco claims to have recorded more than 60 million downloads to Apple’s iOS devices, resulting in 20 top 10 applications, the most popular of which is the Plus+ social network, which has over 13.5 million registered users. It is due to launch games and services for the Android platform beginning this quarter.

DeNA will pay an initial US$300 million for ngmoco, rising by a further US$100 million if the business hits certain performance targets. ngmoco was founded in 2008 by games industry veteran Neil Young (pictured), and has the backing of several investment funds.

According to a Bloomberg report this week, the deal is DeNA’s third involving a US company in the past year, including last month’s purchase of Gameview Studios – a California-based maker of free-play games for mobile platforms.

However, the ngmoco purchase was not immediately well-received by investors in Tokyo, as DeNA’s stock sunk to a two-month low Tuesday after it said it would need to sell shares to fund the deal. The purchase may dilute existing shareholders equity by as much as 5.4 percent, the company said.

“Concerns over the share sale may weigh on the stock in the short term, [but] the purchase is a positive for the company in the long term,” said Atsuo Takahashi, an analyst at Mizuho Securities. “This acquisition fleshes out DeNA’s smartphone strategy and increases prospects for the company gaining market share overseas.”