The social share element is found in article.html

<div class="social-share">
  <p class="title">Share</p>
  <ul class="share-icons">
   <li><a href="#" class="bg-tw"><i class="fa fa-twitter" aria-hidden="true"></i></a></li>
   <li><a href="#" class="bg-fb"><i class="fa fa-facebook" aria-hidden="true"></i></a></li>
   <li><a href="#" class="bg-go"><i class="fa fa-google-plus" aria-hidden="true"></i></a></li>
   <li><a href="#" class="bg-pi"><i class="fa fa-pinterest-p" aria-hidden="true"></i></a></li>
   <li><a href="#" class="bg-mail"><i class="fa fa-envelope" aria-hidden="true"></i></a></li>
  </ul>
</div>

The icons are created with fontawesome

The style can be modified on app/css/scss/elements/_socialShare.scss