Viacom Inc.’s MTV Networks has acquired privately held NeoPets Inc., owner of the teen Web site NeoPets.com., for an undisclosed sum, though the deal has been pegged at $160 million in news reports.

Glendale-based NeoPets, an online entertainment network whose members create and care for “virtual pets” that inhabit mythical lands, gets more than 5 billion page views a month, according to Viacom. To date, more than 25 million members worldwide have created NeoPets accounts in ten different languages. The growth in the user base has mainly been “viral” word-of-mouth from user to user, rather than via commercial advertising.

Doug Dohring, NeoPets.com’s chief executive, and other senior managers will stay on after the acquisition. Dohring will report into Jeffrey Dunn, president, Nickelodeon Film and Enterprises, an MTV unit.

Dohring said aligning with MTV will expand the NeoPets brand offline into television, publishing and movies, such as feature film animation movies based on the site’s 50 original characters.

Viacom also expects the acquisition by MTV Networks, which operates more than 100 channels including VH1 and Comedy Central, should help MTV build its Web audience among kids and young adults. Nearly 60 percent of NeoPets’ visitors are over age 13, the audiences of many of MTV Network’s brands.