Yammer Announces 4 Million Users Last Updated August 28, 2013 By Craig Smith Filed Under: Social Media Yammer announced on their blog tonight that their private social networking tool is now being used by 85% of Fortune 500 companies and has amassed 4 million users. Everyone has a story. We help you tell yours. Begin your journey today... Yammer is a great communication and collaboration tool for enterprise. In case you are not a member of the 4 million users, here is a quick piece I wrote about it last year.