How to make a mobile messenger app popular

Hi,

I have an idea for a kind of messenger app that would be (very basically) like Whatsapp. Problem is, the first users to install the app will want to install it only if they know they have friends and family that use it as well. Otherwise they'd have no one to talk to on the app.

Obviously I'm not the first person to be confronted to this problem, so do you guys know if there's a strategy, method or even "growth hack" to address this issue ? Basically the question is how to get the first users ?

Thanks!