The U.S. mobile advertising market is growing swiftly and will nearly triple this year to more than $4 billion fueled by an uptick in advertising sales at Facebook, Google and Twitter, EMarketer said in a new report.

The U.S. mobile advertising market is growing swiftly and will nearly triple this year to more than $4 billion, fueled by an uptick in advertising sales at Facebook, Google and Twitter, EMarketer said in a new report.