Renren has a blue-and-white user interface that resembles Facebook and carries advertisements for Daimler AG's Mercedes-Benz and China Mobile Communications Corp's phone service. Renren users post messages via a dialogue box in the center of the page and access games, applications and other options on a menu on the left-hand side.

In 2008, Oak Pacific sold a 35 percent stake to investors including Softbank, the Japanese mobile-phone operator headed by billionaire Masayoshi Son, for $430 million.

Renren aims to increase user numbers through its music, wireless and location-tracking services, Li said. The website also aims to boost sales through Nuomi.com, an online commerce affiliate.

Kaixin001.com, with a red-and-white interface, attracted users by focusing on browser-based online games, Chang said. Its most popular games include "Happy Farm", which resembles Zynga Game Network Inc's "FarmVille".

Zhang Shanshan, a public-relations manager for Kaixin001.com, declined to disclose user figures and other operational details.

"Kaixin001.com's core user base is white-collar workers, which is viewed favorably by advertisers," said Jim Tang, a telecommunications analyst at Shenyin Wanguo Securities Co in Shanghai. "Renren.com, because of its background in academia, is used mostly by students."

The similarities between those sites and Facebook illustrate how networking sites in China are generally modeled after the US-based service, said Sabrina Dong, an analyst at Analysys International.

Related readings:  Renren.com to add features  Renren refutes reports of profit decline  Renren.com launches mobile service   Facebook's HK branch to boost presence

Their successes are noted by some of China's biggest Web companies. Tencent, China's largest Internet company by value, launched the social-networking site Pengyou.com last year to attract its QQ instant-messaging service users. The company says it had 636 million QQ accounts as of Sept 30.

Pengyou, or "friend," targets "white-collar" users, said a company spokeswoman.

The site will have trouble luring users from Kaixin and Sina's Weibo micro-blogging service, said Bill Bishop, an independent media consultant in Beijing.

"Tencent is for the masses," he said. "A lot of people who use Kaixin, Weibo, don't want to use a Tencent-sponsored social network."

Baidu, owner of China's dominant search engine, said this month it plans to develop more social-networking services.

"We don't know when Facebook will enter, and what they'll do, but we are confident," Donna Li, general manager at Renren, said. "We want to be the dominant player in social networking."

Bloomberg News