Some companies lose their following after an acquisition, but not Whatsapp — apparently, its userbase just continued to grow after Facebook bought it for $19 billion. The FB-owned entity has revealed that it now has 500 million active users, up 50 million from the time the social network snapped it up. According to Whatsapp CEO Jan Kuom, the app has seen the fastest growth in Brazil, India, Mexico and Russia in recent months.