A good number of those two billion user accounts are not real people. They are either additional alternate identities a person had created, or out-and-out fiction.
Yeah, I'm surprised every time I see that number that it doesn't seem to get much scrutiny. Furthermore, the claim is that they are monthly active users.
Only 1/2 of the planet is even on the Internet. Yet they have 2B MAU?
WeChat has a billion monthly active users, and they managed to do that mostly just in China and a few parts of Asia.
WhatsApp has 1.5 billion monthly actives.
It makes perfect sense that a global social network that dominates in most countries not named China, could get to two billion users.
I must have seen hundreds of skeptical statements on HN over the years about how Facebook can't have X number of users. I've never once seen any supporting evidence against their general scale. Not once, not ever. And again in this thread, skeptics and zero supporting evidence against Facebook having two billion users.
In their favor is extreme data: dozens of large and persistent research efforts put into studying use, by external parties. That spans everything from traditional media usage polling agencies, to large media ratings firms, to ad companies, to competitors, to services that see wide-spread use of Facebook-login, to Web traffic tracking services that indicate massive adoption. It also includes the massive usage that is seen on the iOS and Android app stores. The sole rebuttal possible, is to say: it's all fake! without any equally massive supporting evidence.
Companies like Google would have a very large interest in destroying Facebook by pointing it out, and Google would know as well as anyone if Facebook were lying to such an extreme degree.
I simply do not believe 1/3 of the planet is on Facebook.
I am not. Half of the planet does not have access to clean drinking water, I do not believe they are on Facebook either.