How did you add those icons in the first place? Were they already there when you installed the template?
If so, you'll need to update the code.
In the source code, I can see this:
<ul class="quick-nav clearfix">
<li><a id="rss" title=" RSS Feed" href="http://behindthethrills.com/feed/">RSS Feed</a></li>
<li><a id="twitter" title=" Twitter" href="http://www.twitter.com/BehindThrills/" target="_blank">Twitter</a></li>
<li><a id="facebook" title=" Facebook" href="http://facebook.com/behindthrills" target="_blank">Facebook</a></li>
</ul>
I would look for this code in your theme. Start with the header.php
Then look in the css, for .quick-nav, #facebook, etc ... and simply create new css code for youtube and tumblr.