Apollo has 25m downloads, I can't imagine that the various Android 3rd party apps are any lower than that in total, if not individually.
Officially they make up a small amount of traffic, but amongst power users who both create and comment significantly is much more commonly done through 3rd party apps.
It's not just people missing. It's the efforts of the various organisations around the world that have put huge amounts of effort into finding them when they could've saved a lot more (hell 1 more is a lot more) had they focused on larger disasters.
But because the victims are Arabs and refugees, nobody cares.