Tapjoy and PapayaMobile are announcing a partnership to create a new social marketplace for Android mobile app developers.

The market will be one more way for developers to get their apps noticed in a sea of hundreds of thousands of competing apps. It’s another effort to address the perennial discovery problem associated with mobile app distribution.

Beijing-based PapayaMobile has a mobile social gaming network with 35 million users, while Tapjoy runs a value exchange mobile ad network. The Social Marketplace will let players discover new games and apps based on the popularity within the Papaya social network, and it will make recommendations based on what friends are playing. The market will also deliver more relevant and targeted ads, and developers can benefit from more engagement and increased monetization through the social network.

Rivals include DeNA/Ngmoco, Gree/OpenFeint, and a variety of others. Mihir Shah, chief executive of San Francisco-based Tapjoy, said that PapayaMobile’s social network has the scale and reach across the U.S. and China to make Tapjoy’s ads more targeted and engaging.

Tapjoy’s network has more than 280 million mobile users, who watch videos, subscribe to services, install apps and participate in other kinds of ads in exchange for virtual currency in their favorite apps. It is used in more than 10,000 apps.

“Tapjoy is the industry leader when it comes to ad networks that deliver proven, effective distribution and monetization,” said Si Shen, CEO and cofounder of PapayaMobile. “By teaming with Tapjoy for a Social Marketplace, we’ll be able to offer game developers the very best advertising solution.”