Despite the growing list of literature on governmental social media use, little is known about how different social media message strategies facilitate different types of engagement outcomes (i.e., likes, shares, or comments) and the factors that influence perceived effectiveness of social media use. Drawing on the dialogic communication framework, this study captures these aspects and analyzes data from a public organization in Taiwan, including the content and linguistic analyses of this organization’s Facebook messages over a year, along with interviews and survey with the organization. The data show that the messages aiming to mobilize publics offline and communicated through conversation-style, informal language, and affective and motion words, exemplify dialogic orientation. These messages are positively associated with public engagement on Facebook in terms of the number of likes, comments, and shares. Further, analysis of the interviews and the survey shows that the organization and the targeted publics have mutual and interdependent relationships developed through varied uses of Facebook. Such relationships also influence the perceived effectiveness of the organization’s message strategies intended to foster dialogic communication. Nonetheless, the lack of communication among units within the organization, as well as its bureaucratic culture, result in negative effects for certain message strategies.