Facebook has 3 million advertisers

"Today, three million businesses actively advertise on Facebook. That’s three million companies from all over the world, with more than 70% from outside of the US.
Each of these businesses has a unique story and mission. Whether it’s fashion or fitness, confidence or creativity, each business offers something to its customers and communities that no one else does."
Source:  Blog post from Facebook, 2nd March 2016
Earlier - 2.5m announced in October