The answer to that is yes and no, let me explain - Gillian Flynn based certain aspects of the movie on real life events.
Gillian admits to being a little like Amy (the female star of the film) and claims to have been a sadistic youngster (not sure about you, but I don't think I will be entering any competitions to meet Gillian any time soon!)
Like Nick (the male character in the film played by Ben Affleck) Gillian was also a pop culture writer who was laid off from the company they believed they had a lifelong career with.
As for the rest of the story, and the way Nick was guilty in the eyes of the public without any real evidence, that could be based on so many true life stories over the years in most countries and Gillian has confirmed that is where she got her ideas for the book from.
Apart from that though, the story is original :-)