Global ad spending on social networks to top $4 bln in 2011

In 2007, 37% of the US adult Internet population used online social networking at least once a month. That figure will rise to 49% in 2011, eMarketer reports. 70% of all US teens visit social network sites on a monthly basis. eMarketer projects that worldwide online social network ad spending will grow from $1.2 bln in 2007 to $2.2 bln in 2008, 82%. Worldwide spending will top $4 bln in 2011. In the US, spending is projected to rise to $1.6 mln in 2008, from $920 mln in 2007.