A notifier sends out notifications to potential viewers or listeners of a broadcast stream via social networking systems or other communication channels. The notifier stores information about a user's preferences and identity on the social networking systems. After the notifier receives a notification request from a broadcaster, the notifier commands broadcaster agents deployed in the social networking systems or in the notifier to send notification messages to users of the social networking systems registered to receive notification. The broadcaster agents function as a proxy that establishes relationships with users of the social networking systems and then sends out the notification messages to the users with established relationships.