It has been reported by an author on Buzzfeed that the NBC series Constantine was indeed canceled. Posted in an articled dated April 13th, Kate Aurthur listed the series based on the popular DC Comics character as one of the shows that will not be returning for a second season. That report flew in direct contradiction of what showrunner Daniel Cerone had stated via a tweet on 28 Mar 2015, where he noted the following:
End of April date has been set to pitch 2nd season ideas to NBC. Then they decide on a Season 2.
While many Constantine fans attempted to correct Aurthur, the reporter stood her ground tweeting to series loyalists “I factchecked my renewals/cancellations/bubble post with each network.”
She even went as far as to tweet that it was the “opinion of NBC” that the show was canceled and “I hereby announce that I'm starting to block #Constantine trolls. Focus your energy elsewhere!”
News site ComicBook.com got the official word from Cerone:
I just received confirmation from the corporate offices at NBC. I was assured that Constantine has not been canceled and our pitch meeting to discuss a potential second season remains on the books. By the way, this is a pitch meeting involving the president of Warner Bros and and the entertainment heads of NBC. Nobody at this incredibly busy time of the development season has time to waste taking pointless meetings.
Now, is it fair to say that Constantine is a long shot? Sure, that's fair to say. While we marginally improved a tough time slot for NBC, we're a very expensive show to produce. A lot of NBC's decision making will not doubt hinge on their new pilots and how they feel those new shows would fare as a companion piece to Grimm, versus a second season of Constantine.
Kate then tweeted “#Constantine faithful, my source at NBC tells me your show is still awaiting news. We'll see!”
The original article has now been changed and the series is listed as “Awaiting news.” I would look into getting a new source.