Skysa

Simply set the Twitter account you want users to follow; then, when they click the Twitter Follow button at the bottom of your site, they will start following your account on Twitter. You can optionally set to display your current followers count next to the Twitter follow button and also the language of the Twitter follow button text.
http://www.youtube.com/watch?v=Zj1uGXX2xrk&hd=1 
<a href="https://wordpress.org/extend/plugins/tags/skysa-apps" rel="ugc">More Skysa App plugins</a> -|||- <a href="https://wordpress.org/extend/plugins/skysa-official/" rel="ugc">Skysa App Bar Integration plugin</a>

Skysa Twitter Follow App

Allows your site visitors to follow your twitter account with one click, without leaving your sitet.

Nazmul Hasan Robin

This plugin allows you to show youtube subscribe button anywhere in your website using widget.
Major features in Social Subscribe – Follow Buttons include:
<ul>
<li>Shows youtube subscribe button</li>
<li>Shows youtube subscribers count </li>
<li>Settings from backend to change design </li>
<li>Available in widgets </li>
<li>Other Social Networking Site’s buttons are coming soon!</li>
</ul>

Social Subscribe – Follow Buttons

This plugin provides a widget to show a youtube subscribe button. Also number of youtube subscribers can be displayed.

Skysa Twitter Follow App vs Social Subscribe – Follow Buttons