Chinese Internet giant Sina has reported better-than-expected second quarter 2012 earnings with revenues up 11 percent year over year to $131.6 million and net income jumping from $10 million last year to $33.2 million.

The company said on a subsequent conference call (via Bill Bishop) that Sina Weibo, its popular microblog service, continued strong growth, rising to 368 million registered accounts, compared to 324 million in March, and 36.5 million daily users. Costs for the service, however, rose sharply over the quarter and were the main cause of a $12 million increase in Non-GAAP operating expenses year over year.

Sina, along with other Chinese Internet companies, reported a “challenging macroeconomic environment” in the country during the quarter. Looking ahead to the third quarter, Sina expects revenue between $145 and $148 million, roughly in line with analysts’ expectations.

Shares of the company, which also operates a Web portal, rose 5 percent in after hours trading following the earnings release.

As the Chinese Internet ecosystem continues its rapid emergence, its players are establishing and realigning partnerships. Baidu, China’s largest search engine, recently teamed up with Sina for a partnership. Sina also has plans to release a Weibo-themed credit card with China Merchants Bank that will offer rewards for active Weibo use.

Meanwhile, the microblog space looks to be sorting out as a showdown between Sina and Tencent, as third-place Sohu recently admitted losing over the past two years. For its part, Tencent just posted $1.7 billion in revenue and $491.8 million in profit.  A significant chunk of its revenue comes from the 30 million paying members of its QQ instant messaging platform.

Image via Flickr / bfishadow