Every broadcast television network has lost a significant number of viewers this season -- particularly among the 18-49 age group that most advertisers target, The New York Times reported on Sunday, citing figures from Nielsen Research. Fox, which airs American Idol , has lost an average of 709,000 or 20 percent of its 18-49 demo. ABC has lost 681,000 or 21 percent in that demo. CBS, 239,000/8 percent and NBC 59,000/3 percent. Viewer losses have been accelerating, the newspaper observed, with shows such as Glee, Touch, Missing, and Suburgatory hitting their lowest ratings ever last week. Of particular concern to the networks is the fact that they come just as their upfront selling season is about to take place. "These numbers are going to affect the upfronts," Brad Adgate, head of research at Horizon Media, told the Times . "These numbers represent billions of dollars in sales." Meanwhile, the Wall Street Journal is reporting that some major advertisers, including General Motors and the mobile arm of Samsung Electronics, are planning to shift some of their TV ad budgets to online video sites.