nickgrossman

Enable commenting on your posts via Twitter.
Posts will get a “Discuss on Twitter” button, which will prompt visitors to reply to the original tweet about the post, as well as a “View Discussions” button which will link to existing tweets about the post.
Each new post will be auto-tweeted (requires the <a href="https://wordpress.org/plugins/wp-to-twitter/" rel="ugc">WP to Twitter</a> plugin and a <a href="https://developer.twitter.com/" rel="nofollow ugc">Twitter Developer account</a>).

Discuss on Twitter

Michal Ozogan

This plugin will allow visitor to submit they twitter, while thay are commenting your posts. They account will by showed as twitter follow button.
Registred users can add their twitter account in profile administration.
There is also a setting page where you can edit color, size, showing count and language.
Some themes dont’t use function <code><?php comment_form(); ?></code> to show comment form. In this case you have to edit your template. Find comments.php and add
<pre><code><label for="twitter">Twitter</label><input name="twitter" size="30" type="text" value=''/>
</code></pre>
to form.

Twitter follow button in coments

Allow your visitors to add their twitter.

Discuss on Twitter vs Twitter follow button in coments