Obvious throwaway - this app is fascinating because of its seeming domination of the 'kink' landscape - users move from dedicated forums there to continue chatting and you'll see people's kik names in signatures/tumblr pages all the time.
One reason could be that it uses usernames, and does not tie someones identity to their phone number. So it makes it easier to use in some socially riskier endeavours.
The continued Asian investment in messaging apps like Snapchat (Alibaba), Kik (Tencent), Hike (Softbank), and Viber (Rakuten) is really interesting and makes sense. Apps like WeChat and QQ are extremely popular in the Asian markets, and they want to also have a foothold in messaging services in Western markets.