There is just awesome plugin by Arun [arunshekher]
Quote from its description: (with my English it's easier just copy things).
This plugin converts user mentions (usernames prepended with '@' sign) in comments, chatbox posts, and forum posts to matching user-profile links in your e107 powered websites. It also helpfully renders a username auto completion/suggestion popup-list as you start to type-in a username followed by an '@' sign in plugin supported text areas.
This is one of must to be plugin for any community site. You can download it from Plugin Manager.
You should use this plugin with php 7 or at least php 5.6 .