Earlier this year, BurgerBusiness.com shared data from NPD Group showing that even as the total number of U.S. restaurants declined by 1.1% in 2011, the number of burger restaurants grew. And recently we listed more than three-dozen significant new burger-joint openings in 2012. The burger business keeps growing, and the 13 brands detailed below are among the drivers of that growth. These are small concepts but ones that are adding locations. I haven’t included the growing chains we all know about—such as Bagger Dave’s, Burger 21, Epic, Elevation, Smashburger and the others. Below are 13 concepts you may have missed but that are worth watching because they show what’s happening now in burgers (such as offering craft beers) or because they just might be in your market before you know it.