The top mobile messaging apps tracked by IHS Markit achieved a combined user base of 6.1 billion monthly active users by the last quarter of 2017, up 5% from the previous quarter and 16% year-over-year. The year-over-year growth rate of total users of OTT messaging app has slowed, down from 36% in 2015 and 19% in 2016 as the market matures and smaller players struggle.