Anyone in the art market who was not already paying attention to the social media platform Instagram had to sit up and take notice in late April after the actor Pierce Brosnan visited the showroom of Phillips auction house in London. Mr. Brosnan snapped a selfie in front of a work he admired: the “Lockheed Lounge” a space-age aluminum chaise longue by the industrial designer Marc Newson. Then he added the words “let the bidding commence,” and posted it to the 164,000 followers of his Instagram feed.

And commence it did. Later that week, Phillips broke the world auction record for a design object, selling “Lockheed Lounge” for 2.4 million, or about $3.7 million.

“It’s hard to make a direct correlation between Pierce Instagramming us and the world record, but certainly it made the lounger more desirable,” Megan Newcome, director of digital strategy for Phillips and based in New York, said in a telephone interview. “It was a very exciting sale; we had phone bidders, people bidding online, and there was a lot of excitement around that piece in the auction room. Thanks, Pierce, for the shout out.”

It was not the first time the art market had been influenced by images on Instagram. In the past few years, it has emerged as the social media platform of choice for many contemporary artists, galleries, auction houses and art collectors, who use it to promote art that they are selling and to offer a behind-the-scenes look in art studios, auction houses and art fairs. How much that actually translates into sales like the “Lockheed Lounge,” however, is still up for debate.

Instagram, which started in 2010, is an online mobile app that allows users to share square, Polaroid-style images and 15-second videos, with a network of more than 300 million users worldwide. Users build up their own social networks of followers, and can follow other users, or just “like” images by users they do not follow. Most important for the art world, users are introduced to artists they might like through a “discover” function. Elizabeth Bourgeois, a company spokeswoman, said that globally, users share about 70 million photos each day via the app.

Simon de Pury, an international auctioneer who has 131,000 followers on his Instagram feed, @simondepury, said in a telephone interview: “So many people are either artists, collectors or gallery owners or photographers who are using it very actively, so it allows you to preview exhibitions happening everywhere in the world, and to see the works the minute the exhibitions open, rather than waiting to read about it in a review. That’s what makes it exciting.”

The world’s biggest auction houses, Christie’s and Sotheby’s, also use their official Instagram feeds (with 96,700 and 120,000 followers, respectively) to post preview images of select items from coming sales.

Celebrity collectors and artists are in on the action, too. The pop star couple Jay-Z and Beyoncé Instagrammed their way through Art Basel in Miami Beach a few years ago, posting selfies in front of art they bought or were thinking of buying. Instagram adopters like the Chinese artist Ai Weiwei (with 127,000 followers), the American artist and toy designer Gary Baseman (84,700) and the French “photograffeur” JR (627,000) all keep fans up to date with regularly shared images of new work.

Posting or discovering art is one thing, but the central question circulating around the art world is how many actual art sales are generated by the app. Instagram has no functionality that could make it useful as a direct sales platform, and no plans to add one, Ms. Bourgeois said. But quite often, art aficionados are using the app to preview works of art before they buy.

“When you see something on Instagram that’s hanging in a gallery somewhere and you want to acquire it, you can instantly call up the gallery,” Mr. de Pury said, adding that he had made many purchases this way. “I’m sure that a number of transactions are taking place as a result of works being shown on Instagram. I’m sure it’s quite common by now.”

Just how common it is, however, and who is using the platform in this way is matter of much art world fascination. That is perhaps why, this year, art news websites like artnet.com and hyperallergic.com were abuzz when it was reported that the actor Leonardo DiCaprio, an avid art collector, had bought a painting called “Nachlass” for $15,000 by Jean-Pierre Roy, an emerging artist, over the phone, after supposedly seeing it on Instagram.

Mr. Roy’s dealer, Morten Poulsen in Copenhagen, confirmed that the artist “had posted a detail image of the painting on Instagram.” After that, Mr. Roy received a message from Mr. DiCaprio, “asking us to keep the painting on hold until he saw high-res quality images of the work,” Mr. Poulsen said by email. “I sent him that, the deal was finalized and the painting went into Mr. DiCaprio’s collection.”

Lisa Schiff, an art adviser in New York for Mr. DiCaprio, said he had denied that the sale was based on an Instagram sighting, but she confirmed that Mr. DiCaprio did buy Mr. Roy’s painting through her office just before the Pulse Contemporary Art Fair in March in New York, where it was to go on sale the next day.

Whether or not the Instagram connection was accurate, the report, originally published on the Creators Project, a Vice.com blog, was republished on many top art news websites and blogs as an example of Instagram’s growing market influence. A small survey by Artsy.net, an online platform that both promotes and sells art, bears this influence out, with caveats. In April, the company surveyed 35 known collectors who each had more than 100 pieces of art in their collections and reported that just over half of them had purchased artworks from artists they had discovered on Instagram .

Christine Kuan, chief curator and director of strategic partnerships at Artsy, qualifies those numbers, saying that the platform’s audience is “young collectors and emerging collectors,” who are tech savvy and active on social media.

“A lot of seasoned collectors in the art world don’t use it as much,” Ms. Kuan said in a telephone interview. “They already have their own contacts in the gallery world and they go to art fairs, and may not be using Instagram that way.”

Hearing the results, Ms. Schiff, whose clients also include leading contemporary art collectors like Candace Barasch and Anne Anka, agreed with Ms. Kuan’s qualifications. “No way, no how — seasoned collectors aren’t using it like that,” Ms. Schiff said. “Maybe people in the 20-30 age range, but not over 40.”

Most of her clients are over 40, she added, and in her experience, “online sales for art tend to have a price limit on them of about $20,000, maybe $50,000.”

Anita Zabludowicz, an art collector and arts patron who with her husband, Chaim “Poju,” co-founded the Zabludowicz Collection, which consists about 5,000 works of art by more than 500 artists in London, New York and Finland, the couple’s native country, is an active Instagrammer, with a total of more than 65,000 followers for her three accounts.

Ms. Zabludowicz said she had purchased work based on Instagrammed images, especially from the Brazilian installation artist Adriano Costa and the New York conceptual artist Brad Troemel, which she added to her trove of works by artists such as Damien Hirst, Richard Prince and Nam June Paik.

“Instagram for me is one of the most important social media channels as it is the quickest way to absorb visual information, however shallow,” Ms. Zabludowicz said by email.

She added, however, that she rarely did any actual commerce directly on the app: “If I am working with a gallery, prices would normally be discussed by email or telephone, not via Instagram.”

Ms. Newcome, the Phillips executive, agreed that at least for now, Instagram seemed to be used mostly as a promotional tool, rather than part of “a sales-driven strategy.”

“If one of our specialists has a favorite work in an upcoming sale, they’ll certainly ask for us to ‘give it a little love on Instagram,”’ she said. It’s “a way to create some buzz around a piece. And you never know: you can literally post something on Instagram and a few minutes later have someone ask to buy it. These are the legends that have been developing around Instagram already.”