In its early days, social-networking site Facebook was propelled to popularity by a college-age crowd that sought it out as an exclusive sanctuary in which to connect with their peers. For that market, it was an attractive alternative to sites deemed to have lost their cool — like MySpace, which had become a haven for pre-teens and high schoolers.

Now, it seems, Facebook might be suffering a similar migration. According to comScore, as it has gained a broader audience, the older teens and twentysomethings that drove Facebook’s initial popularity are using it less. And research by WPP Group’s Mindshare suggests that group is reevaluating the site’s worth as a tool for developing friendships. Others believe Facebook’s cool factor among younger users is waning. “When you start getting friended by your grandmother, I think that’s when it starts to lose its cool,” said Huw Griffiths, evp and global director of marketing accountability and research at Interpublic Group’s Universal McCann.

The numbers have fueled a debate among agencies about the implications for marketers. For some, it has raised a warning flag that if the trend continues, clients may have to revise their social-network marketing strategies. Others believe Facebook’s broader growth outweighs any declining usage by the college-age crowd. And still others aren’t convinced that younger users on the whole are less enthralled with Facebook, and believe some may be accessing the site via mobile devices that don’t show up in the comScore numbers.

According to comScore, the average number of minutes spent online with the site among 18- to 24-year-olds fell in September for the third consecutive month compared to the same period a year ago. And the drop-off rate is accelerating. In July, usage fell 3 percent, in August 13 percent and in September 16 percent.
“There’s a ‘parents turn up at the party, the party’s over’ kind of thing going on,” said Mark Potts, North American managing director for consumer insights at Mindshare.

Potts said signs of change began appearing a year ago, when members of Mindshare’s so-called “Scout Network,” a group of trend-spotting consumers scattered around the country, began reporting shifts in the way they and their friends were using the site.

“We began getting comments like they didn’t know how they acquired 300 friends when they didn’t know half the people on the list,” Potts said. Others remarked on the shallow nature of Facebook friendships. “They talked about using it more to coordinate events and gatherings but less so overall,” he said, because of something lacking in the quality of the friendships.

Separately, Mindshare in August surveyed 1,200 consumers about their social-networking habits. More than half of the 18- to 24-year-old respondents (51 percent) agreed that “social-networking sites like Facebook are diluting the quality of relationships.” And 40 percent of that group said they now visit social networks that are based on particular interests, such as TV, music or movies.

The research and trend-spotter feedback led Potts to conclude that younger Facebook users are “adjusting their relationship to it in some fundamental way,” which might call for marketers to adjust their strategies if the trend proves long term.