A Look at the Numbers During 2007, 37% of the U.S. adult Internet population used online social networking at least once a month. eMarketer expects that figure will rise to 49% by 2011. Currently, 70% of all U.S. teens visit social network sites on a monthly basis. Worldwide online social network ad spending will grow 82% from $1.2 billion in 2007 to $2.2 billion in 2008. In the U.S. alone, spending is projected to rise to $1.6 billion in 2008, from $920 million n 2007. Source: Williamson, Debra A. Social Network Marketing: Ad Spending and Usage . eMarketer . December 2007.