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.

Henry Wright

This BuddyPress plugin sends notifications to a collection of members when you use a command to mention them. Supported commands are:
<ul>
<li>@friends</li>
<li>@group</li>
<li>@moderators</li>
<li>@administrators</li>
</ul>

Crowdmentions

This plugin makes it easy to broadcast an @ mention to an exact subset of members.



very useful

Use a command to mention a collection of members on your BuddyPress site.

Comments Users Mentions vs Crowdmentions