Morin Oluwole, the global head of luxury for Facebook and Instagram

Ms. Oluwole runs the business side of the equation: counseling luxury brands on how to use Facebook and Instagram to their financial benefit, and she bills clients like advertising agencies do, based on consumer response, such as clicks per post. She said she doesn’t ever tell brands what the message should be. Instead, she said, “we build a 360-degree communication strategy for brands to share content and drive business value via targeted advertising.”

Louis Vuitton and Dior were the first to grasp Ms. Oluwole’s pitch and sign on. Gucci, Bottega Veneta, Hermès and others soon followed. Her division has grown to 10 staff members in Paris, with satellite offices in New York, London, Milan, Dubai, Seoul, Tokyo and Hong Kong. She wouldn’t say how many brands are advertisers or partners on Facebook or Instagram but “we represent all the major players in the luxury business,” she said.

Ms. Oluwole’s staff creates profiles — compiled from user information, like date of birth, ZIP code, education and work history, favorite music, pages followed — to pinpoint ad targets for brands. For several years, Facebook and Instagram also incorporated information from third-party brokers like Acxiom but such data compilation was banned when the General Data Protection Regulation went into effect in the European Union in May.

Facebook and Instagram were obliged to change their gathering process “across the board” to be compliant, Ms. Oluwole said: “We no longer get information from external sources. We can’t see what kind of car someone bought, because we don’t work with that data provider anymore.”

“Facebook has all this data that you don’t realize they have,” said Scott Galloway, professor of marketing at NYU’s Stern School of Business, and author of “The Four: The Hidden DNA of Amazon, Apple, Facebook and Google.” “They know you better than your doctor, priest and rabbi.”

The problem, he said, is that “bad actors can weaponize that data,” as Cambridge Analytica proved last spring, when the London-based political consulting firm revealed that it had harvested personal data from millions on Facebook — specifics that investigators said swayed elections and Britain’s vote to leave the European Union.

No one is saying that Gucci, Louis Vuitton and Ms. Oluwole’s other clients are involved in anything similar. But it is true that she has built a business, and a lucrative one, on capturing user information and exploiting it to the profit of Facebook, Instagram and their luxury partners. While she would not specify the division’s revenue, she said her division’s piece of the Facebook pie was “quite significant” and added, brightly, “our potential is still large.”

Last year, YouTube hired the “CNN Style” host Derek Blasberg, and Snapchat lured Selby Drummond from her longtime editor’s post at American Vogue; they, too, have been charged with forging alliances with luxury, apparel and beauty brands.

Other platforms have begun to muscle in on Ms. Oluwole’s territory. In August, Ms. Drummond had a preview of Adidas’s Falcon W shoe on a new Snapchat show called “Fashion 5 Ways;” the stock sold out in six hours. Mr. Blasberg teamed with Rihanna to stream her Savage x Fenty lingerie show on YouTube during New York Fashion Week last September; they further amped up the noise by packing the front row with popular social media influencers.

As a result, Facebook is increasing its efforts — or, as Ms. Oluwole said, putting “more functionalities in the pipeline.” IGTV, or Instagram Television, is becoming a more important channel on the app. “Stories” are expanding at Facebook. And there is “Shopping,” a new Instagram tab dedicated to exactly that.

“One day,” Ms. Oluwole said, technology will “create some sort of system that allows you to intelligently guess what the next items are that a consumer wants to purchase.”

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