The glyphicons that come free with Bootstrap 3 is a subset of the full paid Glyphicons library and doesn't include the social media icons set.
Instead, you can use Font Awesome, a free alternative that is fully supported (and the preferred icon kit in Bootstrap 4), which has a free brand icon set:
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-html -->
<link href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css" rel="stylesheet"/>
<i class="fa fa-bitbucket"></i>
<i class="fa fa-digg"></i>
<i class="fa fa-dropbox"></i>
<i class="fa fa-facebook"></i>
<i class="fa fa-flickr"></i>
<i class="fa fa-foursquare"></i>
<i class="fa fa-github"></i>
<i class="fa fa-google"></i>
<i class="fa fa-google-plus"></i>
<i class="fa fa-instagram"></i>
<i class="fa fa-jsfiddle"></i>
<i class="fa fa-linkedin"></i>
<i class="fa fa-pinterest"></i>
<i class="fa fa-reddit"></i>
<i class="fa fa-skype"></i>
<i class="fa fa-soundcloud"></i>
<i class="fa fa-spotify"></i>
<i class="fa fa-stack-exchange"></i>
<i class="fa fa-stack-overflow"></i>
<i class="fa fa-steam"></i>
<i class="fa fa-stumbleupon"></i>
<i class="fa fa-tumblr"></i>
<i class="fa fa-twitter"></i>
<i class="fa fa-vimeo-square"></i>
<i class="fa fa-vine"></i>
<i class="fa fa-windows"></i>
<i class="fa fa-wordpress"></i>
<i class="fa fa-yahoo"></i>
<i class="fa fa-youtube"></i>
<style type="text/css">
.fa {
padding: 4px;
width: 200px;
}
.fa::before {
display: inline-block;
/* .fa-fw */
width: 1.28571429em;
text-align: center;
}
.fa::after {
content: attr(class);
font-family: consolas, monospace;
font-size: 15px;
/* .code */
padding: 2px 4px;
color: #c7254e;
background-color: #f9f2f4;
border-radius: 4px;
margin-left: 5px;
}
</style>
<!-- end snippet -->
For Font Awesome 5, you can still use brands with the separate brands bundle:
<pre><code><i class="<b><i>fab</i></b> fa-youtube"></i></code></pre>