Using SupportMapFragment instead of MapFragment

I am using Xamarin and am learning the SimpleMapDemo sample code for creating a Google Maps application.

The following variable is declared:

private MapFragment _mapFragment;

How can I change this variable to be SupportMapFragment instead of MapFragment?

I am getting this error:

Error CS0246: The type or namespace name 'SupportMapFragment' could not be found (are you missing a using directive or an assembly reference?)

Thanks in advance