Sina Corp, owner of China's largest Internet portal, said yesterday it will invest US$100 million in its microblogging platform Weibo this year as it seeks to build a larger and more influential social media platform.

"We will seek to build up our competitive edge against other service providers and secure our position in the market," CEO Charles Chao told analysts at a conference call.

The company yesterday reported lower-than-expected growth in profit as it boosted investment in Weibo. It invested US$14 million in the first quarter of this year.

Making money from the platform is not a priority in the near term as Sina seeks to spend more on promotions in rural areas, Chao added.

He said at an industry forum last month that advertising, social gaming, real-time search and wireless value-added services may offer revenue channels to the platform.

Sina's first quarter profit fell 38.5 percent from the same period last year to US$15 million while revenue gained an annual 18 percent to US$100 million.

Advertising income in the three months ended March 31 rose 33 percent annually to US$72.3 million but fell 12.3 percent on a quarterly basis.

The company projects revenue to be between US$112 million to US$115 million in the second quarter.

Sina's share price has nearly quadrupled since it launched Weibo in late 2009 that allows users to update their status, upload pictures, videos and lets friends and strangers interact. It will roll out an instant messaging service in the near future as it aims to challenge Tencent's dominant position in the social networking sector.

Sina said its microblog has 140 million users and it hopes to see over 200 million users by the end of this year.