The growth arc of messaging app WhatsApp has been tremendous to watch: 200m monthly active users in April 2013, then 300m in August and 400m in December. Last night, the company announced its latest milestone: 500m active users, meaning it’s added 300m in the last year. No wonder Facebook is buying the company, with CEO Mark Zuckerberg saying he sees the app heading towards 1bn users. “In the last few months, we’ve grown fastest in countries like Brazil, India, Mexico, and Russia, and our users are also sharing more than 700 million photos and 100 million videos every single day,” wrote WhatsApp boss Jan Koum last night. “We could go on, but for now, it’s more important that we get back to work – because here at WhatsApp, we’re just getting started.” Tech site Recode provides some more details on that growth in emerging markets: WhatsApp has 48m active users in India and 45m in Brazil. Koum is also blunt on the efforts of rival messaging apps – several of whom only announce their total registered users rather than actives – to catch up. “There’s not enough money and not enough celebrities in the world to convince people to use a shitty product,” he said.