• by Erik Sass , Staff Writer @eriksass1, October 6, 2011

Global social network advertising revenue will top $5.5 billion this year, sneak past $8 billion in 2012, and approach $10 billion by 2013, according to a new forecast from eMarketer. U.S. social ad revenues will make up just under half of these amounts, coming to $2.74 billion this year and $4.81 billion in 2013, making it the single biggest national contributor of social ad revenues.

The 2013 figure predicted by eMarketer actually constitutes something of a slowdown in the growth rate for social ad revenues, not just in percentage terms but in dollars added as well. After adding $2.5 billion from 2011-2012, the amount of dollars added falls to $1.95 billion in 2012-2013 -- which seems to suggest that social media advertising may already be approaching maturity.

This slowdown is also reflected in social media advertising's share of total ad dollars in the U.S.: eMarketer has social network ad revenues growing from 6.3% in 2009 to 7.7% in 2010, 8.8% in 2011, 10.6% in 2012, and 11.7% in 2013.  In other words, after adding 1.8% share in 2012, social media will add 1.1% in 2013. In global terms, in 2013 social network ad spending will make up 9.4% of total online ad spending.

As might be expected, most of this spending at home and abroad will go to Facebook, trailed at a considerable distance by Twitter and others. However the eMarketer forecast also takes a closer look at advertising revenues for LinkedIn, the first major social network to go public, which needs to demonstrate sustained growth to justify bets placed by early investors.

According to eMarketer, total LinkedIn ad revenues will increase from $140.8 million this year to $200.9 million in 2012 and $249.6 million in 2013. Again, this represents something of a slowdown, as the incremental dollar additions are smaller than the $61.5 million added from 2010-2011.