Drupal does not provide a way to send notifications to all site users by default. The action you are trying to use will only notify the user who triggers the action (you). This module, https://drupal.org/project/messaging, Messaging can help you achieve what you want. You may also need the appbar module.

Drupal does not provide a way to send notifications to all site users by default. The action you are trying to use will only notify the user who triggers the action (you). Messaging can help you achieve what you want. You may also need the appbar module.