KNOWLEDGE WHARTON - Jan 2 - Chinese online dating has taken off and is expected to break two billion RMB ($318M) in total annual revenue by 2014, according to a recent report by Analysys International. China's One-child Policy, rapid urbanization, and the widening gender imbalance have all played major roles in increasing the online-matchmaking market size. The primary players in this space -- Jiayuan, Zhenai and Baihe -- advertise themselves explicitly as marriage websites. Zhenai, a subscription-based dating service, has ~30M users. Despite the impressive size of its user base, Zhenai is maintaining a 40% annual growth rate. Jiayuan's growth is even more staggering. Established in 2003, it acquired 63M subscribers by 2012. Earning more than 44% of the Chinese online dating sector's revenue, the NASDAQ-listed Jiayuan is the only one to have gone public. Despite their impressive growth they face two major business challenges. First, the online dating service industry in China is fragmented. The second challenge is building trust with users.