Engagement across three social media platforms: An exploratory study of a cause-related PR campaign

•This study analyzes a social media public relations campaign promoting the cause of child welfare on blog, Facebook, and Twitter platforms.•Variables examined include social media use, social media engagement, and three intended behavioral outcomes.•An online survey shows that people's use of each social media platform was significantly related to engagement.•Use of each social media platform was also related to all of the campaign's intended behavioral outcomes.•Engagement was found to significantly mediate the relationship between use of each social media platform and offline communication behavior.