Yammer, the rapidly growing enterprise social network, exceeds 4 million corporate users and is rumored to be working on a US$ 40 million funding round.

Cash Action

In September, we wrote about the US$ 17 million in financing that Facebook's former VP of Growth, Mobile and International, Chamath Palihapitiya, helped raise. Now TechCrunch reports that Yammer is working on a new funding round to the tune of US$ 40 million. TechCrunch's Eric Eldon writes:

When I asked founder and chief executive David Sacks about all this, he said that in fact revenues had tripled (although he didn’t disclose any numbers). 'We don’t have any financing news yet,' he explained, 'but given our traction and expansion plans, it’s reasonable to assume that additional financing is likely.'”

Back in 2010, Yammer scored US$ 25 million in funding from four investors and US$ 10 million from the Founders Fund, Charles River Ventures, Emergence Capitol and Ron Conway. Back in January 2009, Yammer landed US$ 5 million in series A financing. You've come a long way, Yammer!

Big Traction

In a recent press release, Yammer announced that more than 85% of the Fortune 500 -- including 7-Eleven, Chevron and General Electric -- now have Yammer networks. Further, more than 100,000 organizations established new Yammer networks in 2011, which brought the total to more than 200,000. Last year also saw record fourth quarter growth, with 32% increase in the average deal size over Q4 2010.

Yammer also enjoyed plenty of moments in the spotlight last year, winning the Management: Collaboration System category in the 2011 Forrester Groundswell Awards with its customer, Deloitte Australia. In the August 2011 Forrester report, The Forrester Wave: Mobile Collaboration, Q3 2011, Yammer was named a Leader in enterprise mobile collaboration. IDC named Yammer one of its Innovative Application Software Company Under $100 Million to Watch, 2011.

User Satisfaction

Last year saw a bunch of enhancements to the Yammer platform, including the release of the Activity Stream Ticker in November. In Facebook-like fashion, the new feature publishes real-time activity in a scrolling side module, highlighting relevant stories, content and third-party business applications.

Yammer Pages, also announced in November, is a service featuring real-time document collaboration, allowing users to create custom, editable wiki-like pages. Yammer also unveiled Files, allowing users to share, follow and comment on uploaded files within the platform's existing social framework.

Earlier in the year, Yammer introduced three business integration tools: Activity Stream and Activity Stream API, Enterprise Extensions to the Open Graph Protocol and Yammer Embed. Soon after, Yammer released the Praise application, allowing users to reward colleagues with badges, as well as a new feature that allows video attachments to play within feeds.

Yammer Connect rolled out in August 2011, providing a bundle of social business integration plug-ins. Based on the Facebook Open Graph protocol, the new Login Button allowed users to bring their Yammer identity, profile information and corporate social graph with them to third-party applications. And Yammer's Javascript API helped developers infuse business applications with Yammer profiles, message feeds and the corporate social graph.

David Sacks, Yammer founder and CEO, says that 2011 was the year that enterprise social networking gained mainstream acceptance. If Yammer was simply enjoying "acceptance" last year, 2012 should be golden for the rapidly growing young social network.