baxeico

This plugin allows to mention WordPress users in a comment by writing usernames preceded by a character (default @), e.g. @guguweb. 
The mentioned users will receive a notification email with a link to the relevant post.
The mention character (default @) can be customized by a filter hook: <code>cum-mention-char</code>. Put the following code in your theme <code>functions.php</code> file:
<pre><code>add_filter( 'cum-mention-char', 'cum_custom_char' );
function cum_custom_char( $content ) {
 return '+';
}
</code></pre>
And the mention character will be +, so you can mention with +guguweb.
This plugin was inspired by <a href="https://wordpress.org/plugins/mention-comments-authors/" rel="ugc">Mention comment’s Authors by Wabeo</a>. Many thanks to the <a href="http://wabeo.fr" rel="nofollow ugc">author</a>!

Comments Users Mentions

Allows to mention Wordpress users in a comment. The mentioned users will receive a notification email.

Simpma

Increase engagement on your WordPress website by adding a Twitter-like mention feature to your comment section.
AtMention in Comments is a simple plugin that makes it possible for comment authors to get notified, whenever they are mentioned in a comment on any post.
<h3>Features of the plugin include:</h3>
<ul>
<li>Mention multiple comment authors in comment.</li>
<li>Mention both registered and non-registered comment authors.</li>
<li>Send notification email to mentioned comment authors. </li>
<li>Customize notification email sent to comment authors.</li>
<li>Customize @mention text color.</li>
<li>Notification email supports HTML.</li>
</ul>
<h3>How to Use</h3>
<ul>
<li>Simply type @ followed by the author name(@john), in a comment to mention the comment author.</li>
<li>Mention authors with spaces in their name by simply replacing the spaces with underscores. Eg: @joh__doe</li>
</ul>

AtMention in Comments

A plugin that enables you to mention @comment__author in comments.

Comments Users Mentions vs AtMention in Comments