Terms of the acquisition were not disclosed.
A statement released by one of Ryzing's investors indicated that Ryzing's team, headed by Manu Gambhir, will join RockYou, which intends to maintain and grow the Philadelphia office.
Wayne Kimmel, a partner in the Artists & Instigators venture fund, said Ryzing currently has 10 full-time equivalent employees, including six in Philadelphia. Kimmel will join the board of directors of RockYou, the company behind the Zoo World line of games on Facebook.
Founded in 2005, RockYou has raised about $125 million from investors including SoftBank, Sequoia Capital, Lightspeed Venture Partners, Partech International, and DCM, according to TechCrunch, Venture Beat and other tech websites.
Ryzing was launched in 2009 by Gambhir, who'd previously developed an online casino site. The start-up's Bingo by Ryzing is available on Facebook. Since its founding, Ryzing had raised about $3 million in venture capital, according to filings with the Securities and Exchange Commission.
RockYou bought Ryzing less than six months after the two firms struck a publishing relationship.
In March, RockYou agreed to pay $250,000 to settle charges by the Federal Trade Commission that it had failed to protect the privacy of users of its online games. Security flaws on the RockYou site allowed hackers to access the personal information of 32 million users, the agency said.