ThinkProgress, a progressive news website founded more than a decade ago, is up for sale, its publisher, the Center for American Progress, announced on Monday. "Unfortunately, like so many other news outlets that have relied on advertising to fund its work, ThinkProgress has seen a significant drop in revenue in recent years, along with other financial strains," Navin Nayak, executive director of the Center for American Progress Action Fund, said in a statement provided to CNN Business. "In addition, events over the last few years have underscored the divergent missions of American Progress and ThinkProgress."