WhatsApp had 1 billion active users per month last year. Now it has 1 billion active users per day. The monthly active users have grown from 1 billion to 1.3 billion. The more interesting metric is the messages sent daily - that's a whopping 55 billion. Add to that the 4.5 billion photos and 1 billion videos shared daily and you've got a very active social network. Source
Source: http://www.gsmarena.com/there_are_1_billion_active_people_on_whatsapp_every_day-news-26425.php
