Twitter Inc (NYSE: TWTR) is expanding its advertising potential to China, according to Reuters, which blocked the service for its citizens in 2009. The company recently opened a headquarters off the Chinese mainland, in Hong Kong, and reports the advertising will be lucrative although they will not be visible to a great portion of people living on the mainland. According to Reuters, Twitter boasted fourth quarter revenues of $479 million with a base of 288 million users. The service is blocked in the mainland due to threats to social order. Other social media sites, like Facebook and YouTube, for example, are similarly blocked, Reuters reported.