FormsPlugin.Iconize.Droid.IconControls.Init(Resource.Id.toolbar);
Plugin.Iconize.Iconize.With(new Plugin.Iconize.Fonts.FontAwesomeModule());

FormsPlugin.Iconize.iOS.IconControls.Init();
Plugin.Iconize.Iconize.With(new Plugin.Iconize.Fonts.FontAwesomeModule())

<key>UIAppFonts</key>
<array>
    <string>iconize-fontawesome.ttf</string>
</array>

<ContentPage ...
xmlns:iconize="clr-namespace:FormsPlugin.Iconize;assembly=FormsPlugin.Iconize" ...
>

<ContentPage.ToolbarItems>
    <iconize:IconToolbarItem Order="Primary" Clicked="..." Icon="fa-search" IconColor="White" />
</ContentPage.ToolbarItems>

<Button  Text="Pesquisar">
    <Button.ImageSource>
         <FontImageSource Glyph="&#xf002;" FontFamily="{StaticResource FontIcon}"/>
    </Button.ImageSource>
</Button>

<ContentPage.ToolbarItems>
    <ToolbarItem>
        <ToolbarItem.IconImageSource>
             <FontImageSource Glyph="&#xf002;" FontFamily="{StaticResource FontIcon}"/>
        </ToolbarItem.IconImageSource>
    </ToolbarItem>
</ContentPage.ToolbarItems>