WhatsApp, which is being acquired by Facebook for $19 billion, has a share button for publishers that has the potential to drive traffic to websites.

Here’s what it looks like:

The company reportedly launched this late last year, and is only testing it with select publishers, including BuzzFeed and Shazam. Liz Gannes at Re/code reports that BuzzFeed is seeing more shares to WhatsApp than to Twitter on iOS, where it displays the button on its mobile web pages alongside other social share buttons from Facebook, Twitter, Pinterest, and Google+.

That’s not to say it drives more traffic to BuzzFeed than Twitter does, but simply, as BuzzFeed told Nieman Journalism Lab, “The metric is that more people click the WhatsApp share button on iOS mobile web than the Twitter button.”

That’s got to be worth something.

Now take into account that WhatsApp has nearly twice as many users as Twitter. Facebook said in its acquisition announcement that WhatsApp has over 450 million monthly users with 70% of them active. By comparison, Twitter said in its earnings report this month that its average monthly active users were 241 million by the end of 2013.

According to Facebook, WhatsApp messaging volume is approaching the entire global telecom SMS volume, and it’s currently adding over a million new users each day. And that was before the Facebook announcement. Look at how Instagram grew after Facebook acquired it.

The obvious difference in sharing content on WhatsApp vs. sharing content on Twitter is that WhatsApp is private. Basically it’s like emailing a link to a friend, or sending them a link through instant message, both of which happen all the time.

WhatsApp’s button will likely be pushed out to more publishers eventually. Right now it appears to only be for iOS. Here’s some documentation for iPhone developers for integrating WhatsApp into apps.

Images via Nieman Lab