In brief: WhatsApp now has more than two billion users worldwide, joining an elite group of platforms that have eclipsed that same milestone. As even more users come online, the figure is likely to continue to grow although perhaps not at the same pace it has enjoyed up to this point.

WhatsApp's growth has been nothing short of impressive. Initially launched into beta in January 2009 by former Yahoo employees Brian Acton and Jan Koum, the communications app found an early following and by 2011, it was among the top 20 apps in the US App Store.

Serious money from investors started flowing in at that point, as did more users. In December of 2013, the startup said it had more than 400 million monthly active users. This helped attract the attention of potential suitors and in mid-February 2014, Facebook pulled the trigger, agreeing to acquire the company for a cool $16 billion.

It's only been onward and upward for Facebook and WhatsApp since that point.

Facebook now owns and operates some of the world's largest apps including the Facebook standalone app, Messenger, WhatsApp and Instagram, the latter of which it scooped up for a bargain at just $1 billion in 2012.

Reports from just a couple of years ago suggested Facebook was falling out of favor with some demographics but that hasn't seemed to slow the growth. In its most recent earnings report, Facebook said it now has 2.5 billion monthly active users, an increase of eight percent compared to the same period a year earlier.

Masthead credit: WhatsApp by Antonio Salaverry. Social apps by Wachiwit.