San Francisco-based Social Express, a developer of social games, has been acquired by MTV Networks. According to MTVN, which is a unit of Viacom, the acquisition will provide it entry into the social gaming space. Financial terms of the buy were not disclosed. MTVN said Social Express will become part of its Nickelodeon Digital unit, with Social Epxress founder and CEO Tony Espinoza becoming VP and GM of Social Gaming. Co-founder Neil Souza becomes VP of Technology, Social Games.