Many online media companies still see their websites as cornerstones of their business, because that’s where they make most of their money. But more and more, people are reading news stories and watching videos off of the original publisher’s sites, on social networks like Facebook.

For an online publisher, seeing what users are doing on their site is fairly easy to do with tools like Chartbeat and Parsley and Omniture, which measure various kinds of activity.

But tracking all of the social engagement for content that’s happening on external networks and services like Facebook and Twitter is much more difficult.

To try to solve that problem, Chartbeat is rolling out a new feature called Offsite Social, in partnership with social-analytics company CrowdTangle.

In the same way that Chartbeat gives publishers a dashboard through which they can track exactly what readers are doing on their site—how long they spend with an article and what links they clicked on, etc.—the new feature lets them see who is sharing their content and where, and what kind of traffic it is driving.

“Many of the publishers we talk to say they have this social news gap, where they see spikes happening on Facebook or wherever and they don’t know why,” Chartbeat CEO John Saroff said in an interview before the launch. “We’re trying to fill that gap.”

Over the past year or so, mobile and social traffic has started to play a much larger role for most online publishers. Some media companies have leaped head-first into this world—BuzzFeed says more than 75% of what it produces never appears on its website.

And paying attention to that activity could become even more important as advertising for desktop internet users continues to decline with the shift mobile devices. According to a recent study by ad firm Publicis, desktop ad revenue is expected to fall substantially over the next two years.

The social part of Chartbeat’s new dashboard is powered by CrowdTangle, which tracks millions of individual accounts on social networks such as Facebook, Twitter, Reddit, YouTube, and Instagram. If a link is shared, CrowdTangle reports where and by whom.

“There are lots of fairly robust tools that help publishers track every activity on their website, but tracking these other social sites is hard,” said CrowdTangle CEO Brandon Silverman. “And then people have a massive spike in traffic because it takes off on Facebook and they don’t know why. This helps them understand that.”

Other social analytics services can show how much traffic a site gets from a specific network like Facebook or Twitter, Saroff said, but only CrowdTangle can show the sharing activity on an article-specific level, so publishers can see which articles are producing the greatest response.

Being able to see at a glance who has shared a specific piece of content and where will help media companies understand which communities of interest they are reaching, Saroff said. And then they can reach out to those users in a variety of ways.

“We’re hoping this will help folks at media companies get a deeper picture of what’s happening to their content on social network,” the Chartbeat CEO said. “And then they can take action to engage with that audience and maybe get them to come back to their site.”