Detect a tap and add a pin to the map?

I'm new to Xamarin, and am developing an application that will use a map. We're using Xamarin Forms, and I am able to properly get a map displayed. I can scroll around, etc.

I want to simply detect a tap and drop a pin where the user tapped, but I can't seem to get the Map to detect that it's been tapped. I've tried adding a GestureRecognizer to the Map, but that doesn't seem to help.

Is there a way, using Xamarin Forms to do this in a cross-platform manner? Or will I have to implement this functionality twice, once on Android and once on iOS?