This study focuses on social media use by law enforcement agencies. Based on media richness theory, we examined how the responses to Facebook messages posted by five police departments vary by type of cue, image vs. text, and across different content categories. Our findings suggest that although messages with richer information, namely more visual and verbal cues, receive more likes, topics such as Accident, Traffic and Announcement receive significantly fewer likes. Moreover, the presence of pictures in announcement messages reduces the number of likes. In addition, although people comment on messages about Property/Pets, they are much less inclined to comment on other topics. Our study contributes to media richness theory by demonstrating the importance of considering the nature and context of a communication, as represented by the content category, and to law enforcement agencies' practice by offering recommendations for how to measure public engagement and design strategies that will better leverage social media.