• by Wayne Friedman , March 4, 2011

In the digital world, this may be a no-brainer: Now, virtually all U.S. teens are using the Internet, far outpacing the total U.S. population. More importantly, many are counting on social media to influence their purchasing decisions -- a key factor in future advertising budgets and campaigns.

By the end of 2011, eMarketer says 96% of American teens ages 12 to 17 will use the Web at least monthly, much higher than the 74% penetration for the total U.S. population. Teens will inch up to 97% in the coming years through 2015, then remain at that level. Overall Internet usage among all population groups will climb more rapidly, rising to a 79% penetration by 2015.

Social networks are a major factor in growth. More than four in five teens -- 80% -- will use social networks this year. That compares to 64% of all Internet users.

Just considering Facebook, nearly three-quarters of teens will use the giant social media platform at least once a month this year. This compares with over 50% who used the site daily in 2010.

Another survey, from Ipsos Public Affairs, says 70% of teens use Facebook weekly. More research from Roiworld and OTX says that as of last June 2010, 69% of 13- to-17-year-olds have a Facebook profile.

All this social activity is increasingly critical to retailers. More than 4 million teen girls purchased items online in 2010, up from 3.4 million in 2009 -- a 52.6% gain.

"Peer influence is the key driver in teen girl shopping behavior," stated Tobi Elkin, eMarketer writer/analyst. "While they are price-conscious and driven by a great deal, teen girls weigh these factors against the all-important consideration of whether peers will approve of their purchases."