With the London summer Olympics just 100 days away, advertisers hope that social media will do much of the heavy lifting in raising brand profiles, by getting consumers to chat about promotions online.

Big consumer brands have long seen the Olympic Games as a way to get more consumers to buy their products. This year, several are thinking of them as a way to talk up their brands on Facebook — which of course could lead to even more purchases.

The games run from July 27 to Aug. 12 this year.

“Back in 2008, it was very much about paid media,” said Mark Renshaw, chief innovation officer at Leo Burnett, a unit of No. 3 advertising agency Publicis, referring to the last summer Olympics. “Now the reason they want to have a relationship (with consumers) is to generate shared media.”

That’s in part because of the sheer amount of time people are spending on social media. By the end of last year, some 794 million people visited Facebook each month, and each spent an average of 377 minutes — more than 6 hours — on the site, according to comScore Inc.

In 2008, Facebook had just 145 million users. Online marketing then focused on building websites, Renshaw said. Today, brands are building elaborate campaigns partly designed to create a buzz on Facebook and other social media sites such as Pinterest and Twitter.

Take Samsung Electronics, which recently launched its US Olympic Genome Project. It uses a game called “How Olympic Are You?” to establish people’s connections to the Olympics, such as finding athletes from their hometowns, or athletes who like the same music or movies they do.

It gathers the information by tying in to a user’s Facebook page. The game dangles prizes such as discounted electronics and a trip to the Olympics to keep consumers coming back; whenever consumers complete an activity, such as a quiz on Olympic trivia, they are invited to post results to their Facebook page.

Facebook “is where consumers are,” said Ralph Santana, chief marketing officer of Samsung. “If you can figure out how to build communities around your brand, it’s really powerful.”

Consumers are spending about 8 minutes per visit, on average, on the “How Olympic Are You?” site, Santana said. That is about double the time they spend on ordinary Samsung sites.

Social media “drives us toward content that is able to provoke consumer conversation,” said James Eadie, Olympic portfolio director for Coca-Cola Co. “That drives longevity.”

Coke’s Olympic gambit is its “Move to the Beat” campaign based on a song created by DJ Mark Ronson and singer Katy B. Fans can collect beat fragments on Facebook and edit a version of the song for their own page.

Procter & Gamble this week unveiled its “Thank You Mom” advertisement showing mothers around the world raising Olympic athletes. Marc Pritchard, P&G’s global marketing and brand building officer, is hoping online viewers will “like” the video on Facebook and drive traffic to its own Facebook pages for brands like Tide detergent, Pampers diapers, Oil of Olay moisturizers, and Cover Girl cosmetics.