While the influx of free and low-cost video has hurt the sale of pornographic videos, the chief executive of the Penthouse Media Group remains so bullish on the sex-related entertainment industry that he is investing $500 million in a group of social networking sites.

Marc H. Bell, chief executive of Penthouse Media, said the company had acquired Various Inc. and its subsidiaries as part of a plan to expand its reach. Various operates more than 25 networking sites and says it has a member base of more than 260 million consumers, about 1.2 million of them paying subscribers.

The combined revenue of both companies is projected to be $340 million in 2007.

Various’s most popular Web site is adultfriendfinder, which describes itself as a personals community for swingers and sex. But Various owns a variety of other social networks like Italianfriendfinder.com, gradfinder.com and bigchurch.com, which offers to help users “meet people who share the same spiritual beliefs as you.”

“For now, we are holding on to everything,” Mr. Bell said. He said the goal was to provide consumers, particularly 18-to-34-year-old men, with a wide variety of sex-related offerings in magazines, in videos and online.