If you’re going to capture anybody’s attention, you need to do it where they’re spending their time. Increasingly, that’s social networking sites. According to a study from research company NetPop, time spent social networking has exploded 93% since 2006. That means around a third of the time U.S. Internet users spend online is devoted to communicating, not consuming.

Dig deeper into these social networking activities and you find out that people communicate online each week with, on average, 18 people one-to-one and with 110 people through group interaction. And this isn’t just kids, the usual justification for dismissing the importance of social media. Of active social networkers (those who have estalbished profiles on more than one site) 25.6% are between 18 and 24, 23% are 25 to 35, but nearly half are 35 to 64.

The study, “Online Activities among U.S. Broadband Users, 2006 and 2007 (U.S. $295),” reported that 76% of American broadband users are “joiners,” to use the parlance of Forrester’s technographic ladder. That translates into 105 million people in the U.S. communicating through social sites like Facebook, MySpace, and LinkedIn, not to mention niche networks and social networks (like CarSpace and MyRagan) and social networks integrated into broadere sites (like FastCompany).

More time on social networks means less time spent elsewhere, and Netpop’s research suggests that reallocation of time comes at the expense of more traditional online entertainment. Passive consumption of entertainment online droped 29% over the last two years, to just 19% of the time people spend online. Another way to look at this: Peoples’ idea of what constitutes entertainment is shifting from passive consumption of online media to a more active engagement with other people, mostly people they already know. Sharing with others is more fun than kicking back and watching a video.

According to Netpop, the study suggests that companies need to do more to engage consumers and commit more of their online efforts to user-generated content and social media through which people can talk with the company and with each other. If companies don’t provide these opportunities, they will find it harder to track and engage consumers because, Netpop believes, they’ll find other channels through which they can participate in such conversations, even if it means building those communities themselves.

It’s easy to dismiss the notion that cmpanies must build community around their brands, but trying to caputre attention by hitting people with messages in places they’re not spending time is like shoving wads of money into a garbage disposal. I’m currently reading Martin Lindstrom’s excellent book, “Buyology,” in which he provides compelling evidence that people don’t pay attention to brand messages in video games, for example, yet companies are pouring exorbidant sums into in-game marketing. Business needs to understand that consumer habits across a loarge demographic swath are changing, and thus the means by which to reach them have to change as well.

The blog Bohan Style offers a good example with Victoria’s Secret Pink, a Facebook group into which more than 1.1 million people have opted. The post quotes Brad ABettese, executive VP and managing director of a Sanfrancisco marketing agency: “The community is a self-selecting loyalty program. Pink has been careful to provide tools that not only help to manage the brand’s identity, but communicate with loyal ‘friends’ and strengthen the brand’s relevance.”

The decision to deliver value through authentic engagement seems less and less optional in the face of ia growing body of evidence. I’ll be including Netpop’s numbers into my upcoming presentations.