Fake news are not just limited to FB, you can find them on every news website.
For an increasing number of people, particularly Americans, Facebook is becoming the primary source of news coverage.
The site's News Feed is specifically designed to show users content it thinks will be of most interest, creating what some describe as a "filter bubble" that reinforces a person's view without injecting differences in opinion. However, a large portion of these news which are "trendying" on FB and get shared a lot turn out to be fake, and come from fake news websites, who only post this nes in order to collect ad revenues from website clicks. In fact some data has shown that fake stories were being far more widely shared on the platform than follow-up stories debunking the claims. However this is not to suggest that "real" news from mainstream media outlets are are not fake or misleading as well. The venerable New York Times had to apologize to its readers over its blatantly distorted and one sided coverage of the US 2016 presidential elections and how it demonized Donald Trump. FOX news had to apologize after running a fake story falsely reporting that Hillary Clinton faces indictment by the FBI over its Clinton foundation investigation. CNN apologizes for posting false news and incorrect stories almost on a daily basis. But at least these news medias sometimes apologize for their fake stories and news. News outlets like "Breitbart", "Huff Post", "RT", "AJ+", "Info Wars" don't even bother to do that because the amount of bullshit and lies they post on their websites, on a daily basis, is mind boggeling. So be sure to watch out for fake news on FB, and everywhere else on the internet.