Social networks have come a long way since Friendster, MySpace and Facebook jump-started one of the hottest online trends in the past decade.

A new Pew Internet & American Life Project report indicates that social networks have made great inroads with adults in the United States but still are predominantly the domain of teenagers and young adults.

According to Pew’s report (PDF), more than a third of adult internet users in the United States now have a profile on at least one social network. In 2005, only 8% did. Because adults make up a greater percentage of the population, there are actually now more adults on social networks than teenagers.

In percentage terms, teenagers and young adults still dominate – a whopping 65% of teenage internet users are on social networks and 75% of internet users ages 18-24 are on social networks. The numbers go down from there. For instance, only 19% of the internet users 45 to 54 years old have a profile on a social network. That number decreases to 7% for those over 65.

Of course, this data isn’t surprising to anyone who has followed the market and watched the explosive growth of services like MySpace and Facebook. But Pew’s report does contain some additional insights that have implications for digital marketers and online publishers who may be involved with social networking in some fashion:

  • The vast majority (89%) of social network users use them to keep in touch with friends. Far fewer use sites like Facebook for professional purposes. For digital marketers looking to leverage these networks as marketing platforms, the challenge is finding a way to engage users appropriately in what is really a very personal environment for most.
  • There’s some fragmentation, as just over half of the users have more than one profile and 83% of these users have those profiles on different social networks.
  • Where you are in life‘ seems to play a significant role in social network usage. Pew reports that “68% of full time students and 71% of part-time students have a social network profile, while just 28% of adults who are not students use social networks.
  • While there is no significant difference between the number of men and women using social networks, there are some demographic differences. For instance, those with annual incomes of $75,000 or more and a college degree are less likely to have a social networking profile than those who make $30,000 – $49,999 and have some college education.

    Demographics vary between social networks. For instance, “MySpace users are more likely to be women, Hispanic or black, to have a high school education or some experience with college.These sorts of demographic nuances are important for digital marketers to look at when evaluating social media campaigns.

  • 60% of the adults on social networks restrict access to their profiles. This number is higher on Facebook (79%) and MySpace (63%). A similar number – 58% – restricts some portions of their profiles. This highlights the challenges digital marketers face in reaching these users; the large number of restricted users demonstrates the personal and private nature of these networks.