SINA Corp, operator of one of China's largest portal website and popular social platform Weibo.com, said yesterday it will continue to invest to develop the Twitter-like microblog service even after it posted the largest quarterly loss.

The company's advertising revenue climbed but the rise was overshadowed by increasing costs in product development and marketing fees as well as a write-down of its equity investments.

"We intend to make significantly more investment in product development and marketing for Weibo in the next few quarters to accelerate new product launches and accumulate more users in order to maintain our leading position in the social media sector," Sina Chief Executive Officer Charles Chao said in an earnings conference call yesterday.

Weibo.com has around 250 million registered users by the end of September, and it has been adding value-added services including online gaming and virtual currency over the past few months.

Sina hopes to make money from adding advertisements and e-commerce applications to Weibo in the long term, Chao said, without elaborating.

Chao said earlier this year the company will invest US$100 million in Weibo in 2011.

Sina reported a loss of US$336.3 million, or US$5.10 a share in the third quarter ended September 30, compared with a profit of US$31.3 million in the year-earlier period.

Income in the three months rose 20 percent from that of a year ago to US$130 million.

Write-downs on Sina's investments in online apparel retailer Mecox Lane and real estate portal website China Real Estate Information Corp totalled US$281 million in the third quarter.