This article seeks to explain variation in news sharing patterns on social media. It finds that news editors have considerable power to shape the social media agenda through the use of “story importance cues” but also shows that there are some areas of news reporting (such as those related to crime and disasters) where this power does not apply. This highlights the existence of a social “news gap” where social media filters out certain types of news, producing a social media news agenda which has important differences from its traditional counterpart. The discussion suggests that this may be consequential for perceptions of crime and engagement with politics; it might even stimulate a partial reversal of the tabloidization of news outlets.