WeChat 1.0 came out on January 21, 2011, with only four functions. By May it had added voice messages, and in August “People Nearby.” By the end of 2011, it had more than 50 million users. In March 2012, it passed 100 million.
Version 4.0 came out in April 2012. One source dates it to May. Video calls followed in August 2012, and payment in August 2013.