According to the article, it sees a drop in usage among teenagers while  there are increases in numbers of users of many mobile apps such as  We chat and Vine.

Mobile phones are playing an increasingly important role in people’s life. There is no denying that large population in China contribute to the boost in usage of We chat among teenagers. However, although Facebook can be installed on cellphones, people cannot use it to send voice messages. Comparing to texts, voice messages can convey information more accurate and fast. Pictures can also be sent immediately to friends.  In addition to this, teenagers often wants to share something only with their close friends and would like to  receive replies soon, and mobile apps like We chat can meet their requirements.

http://www.forbes.com/sites/parmyolson/2013/11/12/heres-where-teens-are-going-instead-of-facebook/