Example of how implement share text and links in Xamarin.Forms applications. - http://julianocustodio.com/share-xamarin-forms

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:ShareDemo"
             x:Class="ShareDemo.MainPage">
    <ContentPage.ToolbarItems>
        <ToolbarItem Icon="share.png" Clicked="Share_Tapped"/>
    </ContentPage.ToolbarItems>

    <StackLayout>
    	<Image Source="logo.png" 
           HorizontalOptions="Center"
           VerticalOptions="CenterAndExpand" />
        <Label Text="www.julianocustodio.com" 
           HorizontalOptions="Center"
           VerticalOptions="CenterAndExpand" />
    </StackLayout>

</ContentPage>