• by Steve Smith , Staff Writer @popeyesm, April 4, 2013

The ambitious and apparently successful entrance of both Facebook and Twitter into the mobile advertising field in 2012 helped increase mobile ad spend 178% last year -- and will push it another 77.3% this year, to approach $7.2 billion. This is according to eMarketer’s latest forecast for marketing spend across mobile display, search and messaging. The metrics include both mobile and tablet spending.

Facebook has quickly become a powerhouse in the space, now standing as second only to Google in mobile ad revenues. eMarketer is showing that the social network earned over $390 million in mobile ad revenue in 2012 and expects it to more than double to about 965 million this year. Likewise, Twitter -- which is right behind Pandora as the fourth-largest mobile revenue generator -- earned just under $135 million in 2012, which will almost double to $264 million in 2013.

Google, of course, continues to dominate the field with more than half of all mobile ad revenue going to the search company. Despite the gains of both Facebook and Twitter, Google will maintain its market dominance for years to come. eMarketer expects that growth in mobile advertising for YouTube will be one of the places where Google will be able to expand its mobile revenue even as its growth in search and display may ease. Meanwhile, Facebook’s share of the mobile marketing pie will exceed 13% this year.

While the research company's projections for Facebook and Twitter were considerably brighter than previously forecast, much of their gains in market share appears to be at the expense of the rest of the mobile ad network ecosystem. While Millennial Media -- the largest independent ad network in mobile -- had 6.6% of the market in 2011, that share is seen dropping to well below 3% this year and moving forward.

Looking farther down the road, eMarketer is expecting mobile advertising in the U.S. to exceed $16 billion in 2015.