Robin Li yesterday passed Wang Jianlin as the richest person in the mainland by US$63.6 million, according to the Bloomberg Billionaire Index. The founder of China's largest Internet search engine, Baidu, has become the wealthiest individual in the world's second-biggest economy, 14 days after he took the No 2 spot. Li's net worth has climbed by US$4.8 billion, or 65 per cent, to US$12.23 billion so far this year as Baidu shares rallied. Wang, chairman of closely held Dalian Wanda Group, has seen his fortune rise by US$2.9 billion to US$12.2 billion. Wang may reclaim top spot after he sells shares in AMC Entertainment Holdingsm, the US cinema chain he bought for US$2.6 billion in 2012. AMC this week said it plans to raise as much as US$368 million in an initial public offering. Quick expansion in smartphones and tablets plus a predominant position in the desktop search market have boosted Baidu shares 69 per cent in the past six months, says Lucy Zhang, an analyst at internet consulting group IResearch. "Baidu's development on mobile has surprised the market and its search app's traffic volume has been growing very fast," Zhang said from Beijing, where Baidu is based. Baidu had an 81 per cent share of search-engine queries in China in the three months ended June, followed by Qihoo 360 Technology with 10.1 per cent, according to data. Baidu's market share for desktop search has been stable as threats to its dominance faded after Qihoo failed to acquire Sohu.com Inc's search engine Sogou, Zhang said. Baidu, whose name is derived from a Chinese poem from the Song dynasty, was co-founded by Li on January 1, 2000 in Beijing's Zhongguancun, China's equivalent of Silicon Valley. The company, which has grown from fewer than 10 staff to more than 17,000 today, sold shares on the Nasdaq in 2005. The bulk of Li's wealth comes from his 20.8 per cent stake in Baidu. The shares are owned directly by Li and his wife Melissa Dongmin Ma through Handsome Rewards, a British Virgin Islands-based holding company. The 45-year-old billionaire also owns 1 per cent of 360buy Jingdong Mall, a closely held Chinese online retailer that had revenue of US$3.9 billion in 2012. Li, who is also known as Li Yanhong, said in October that his company would continue to invest aggressively in mobile search. Its search app installments rose 50 per cent to 330 million users by the end of September, compared with three months ago. "We probably invested a lot more than any of the competitors in the mobile-search front," Li said at an earnings call. "This year and next year will be very, very crucial for the eventual success of the overall mobile strategy." The internet company agreed in August to pay US$160 million for 59 per cent of location-based e-commerce service Nuomi Holdings and said in July it would buy app store 91 Wireless Websoft for US$1.9 billion. It bought Santa Clara, California-based TrustGo Mobile for its security and personal-privacy protection technology earlier this year, Li said in a televised interview with Bloomberg West , without disclosing details. Baidu is also exploring opportunities on internet finance. In October, it offered Baifa, a money-market fund managed by China Asset Management. The product has attracted more than one billion yuan (HK$1.26 billion) of investment from more than 120,000 customers on its debut, according to Baidu spokesman Kaiser Kuo.