ToolbarItem icon in WP don´t show

I am doing this

if (Device.OS == TargetPlatform.WinPhone)
{
    tbi = new ToolbarItem("add", "Toolkit.Content/ApplicationBar.Add.png", () =>
    {
        var todoItem = new TodoItem();
        var todoPage = new TodoItemPage();
        todoPage.BindingContext = todoItem;
        Navigation.PushAsync(todoPage);
    }, 0, 0);
}

in my PCL, and the folder Toolkit.Content has the ApplicationBar.Add.png image, but is not showing it in WP app.