The following code may work:
<a class="social_icon" target="_blank" style="margin-top:-2px;" href="http://www.yelp.com/biz/zain-elmarouk-crossfit-415-san-francisco"><img src="[siteurl]/images/yelp.png"></a>
If that doesn't align it the way you need, then you can adjust the margin until it aligns correctly.
Technically, this is considered custom coding, and isn't officially covered by support.
I recommend checking out the Codecademy HTML and CSS course
to learn the basics of how HTML and CSS work; it's free, and if you combine that with Firebug
, you should be able to figure a lot of things out on your own, which is generally faster than waiting on support.