In a roundabout marrying of data sets, Google search intent can now be harnessed for Facebook ad targeting.

It's a fresh take on Facebook's "custom audiences," where marketers have been able to target their customers on the social network via their existing trove of email addresses and other data, or retarget visitors of their websites and mobile apps via a Facebook pixel on those pages.

Now they can also target to people who have clicked on their search ads on Google, Bing and Yahoo, effectively bringing together social and search-intent data. It means search advertisers can chase leads on Facebook.

"You're getting one of the most complete pictures of customers that's ever been assembled," said Will Martin-Gill, senior VP-product at Kenshoo, the digital-marketing firm that developed the targeting tool together with Facebook.

The tool allows for big performance marketers who've invested in building out their search campaign architecture to chase down leads on Facebook. Hypothetically, Cadbury could target ads to Facebook users who've already clicked on Google ads yielded by searches for "chocolate," "Easter egg" and "Easter Bunny" -- terms that signify a high degree of interest in their product, especially once a click has ensued. Facebook's demographic and interest-level targeting parameters can also be applied to refine the audience.

The targeting tool functions via an anonymous cookie sync that starts the instant a person clicks on an advertiser's search ad -- when that brand is able to begin tracking the user -- and the corresponding user's Facebook ID. No participation was needed from Google or the other search engines, since brands are able to track people who have clicked on their ads.

Thus, not surprisingly, Facebook and Google didn't work together on the product, and while it's designed to give advertisers yet another way to spend money on the social network, Google and the other search engines don't see any return from it.

There are potential savings for marketers looking to re-engage prospects -- especially those targeting expensive keywords on Google -- if they follow them onto Facebook, according to Mr. Martin-Gill.

"You've already paid the high click-through on Google," he said. "If you can [then] get to them with a Facebook ad, you have a less expensive way."

While Kenshoo is the first Facebook ad partner to enable this kind of targeting, more may come. A Facebook spokesman confirmed that while the company helped Kenshoo build its technology, the cookie-sync capability that makes it viable is not exclusive to Kenshoo, and other ad partners may build out their own versions.