I find that social sharing buttons are a real pain, primarily because they are not designed to integrate seamlessly with your design. Twenty Fifteen doesn’t have any social sharing options at all. I opted to provide options to integrate them into your posts. Of course, this is just an option, you can still use the plugin of your choice if you prefer.
Where to Find It?
Customizer > “Social Sharing”
Choose which social sharing channels to add to all your posts. Sharing buttons are fully responsive, integrated seemlessly with “Ridiculously Responsive Social Sharing Buttons”.
Also choose whether the buttons are at the top, bottom, or both positions within the post. Each post on this site shows the buttons in both positions.
See it in Action
This site has all the available channels enabled and has them at the top and bottom of all Posts.
Here you can see how they can appear live in the Customizer. You just need to navigate within the Customizer to a post in order to see them enabled live.