Tencent Holding Ltd was listed on the Hong Kong Stock Exchange on 16 June 2004,[23] and it was added as a Hang Seng Index Constituent Stock in 2008.[29] The company originally derived income solely from advertising and premium users of QQ, who pay monthly fees to receive extras.[22] But by 2005, charging for use of QQ mobile, its cellular value-added service, and licensing its penguin character, which could be found on snack food[30] and clothing,[22] had also become income generators.[22] By 2008, Tencent was seeing profit growth from the sale of virtual goods.[31] While Tencent's services have included online gaming since 2004, around 2007/2008 it rapidly increased its offerings by licensing games.[32] While at least two, CrossFire and Dungeon Fighter Online, were originally produced by South Korean game developers, Tencent now makes its own games.[32] On 21 January 2011, Tencent launched Weixin (微信), a social media app.