Facebook lost 400,000,000 users to China's social network ?

WeChat has more than 700 million users worldwide, most of whom are in China

At the time, two social networks proved to be the most popular – QQ and WeChat – while the microblogging platform Sina Weibo, arguably the more famous network outside of the country, had far fewer users.

http://www.bbc.com/future

I read that you can buy 50,000 facebook users for $4000. Does the numbers shown for facebook are real or bots. There are 2,800,000,000 to 3,000,000,000 internet users worldwide.