WhatsApp Messenger has finally included a mention feature that allows users to mention other users ina group chat.
The
Mention feature allows you to address a contact inside a group chat to get their attention.
Weather online or offline, the contact will get a notification of the mention.

To use this feature, When in a group chat press the
@ symbol on your keypad.
A list of users available in the group will be displayed for you to choose.
Make sure you Update your Whatsapp to the latest:
WhatsApp beta v2.16.272