<maps:Map x:Name="Map">
    ...
</maps:Map>

var position = new Position(37.79762, -122.40181);
Map.MoveToRegion(new MapSpan(position, 0.01, 0.01));
Map.Pins.Add(new Pin
{
    Label = "Xamarin",
    Position = position
});

((ViewModels.YourViewModel)BindingContext).PropertyChanged += yourPropertyChanged;

private void yourPropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if(e.PropertyName == "YourPropertyName")
    {
        var position = new Position(37.79762, -122.40181);
        Map.MoveToRegion(new MapSpan(position, 0.01, 0.01));
        Map.Pins.Add(new Pin
        {
            Label = "Xamarin",
            Position = position
        });
    }
}