This study examines the Twitter utilization practices of the 100 largest nonprofit organizations in the United States to understand how they use micro-blogging for communication and engagement. The analysis reveals three key functions of micro-blogging updates: "information," "community," and "action." While informational use is extensive, nonprofits are better at using Twitter to engage stakeholders through dialogic and community-building practices compared to traditional websites. The study proposes an "Information-Community-Action" micro-blogging message classification scheme and classifies organizations into three types: "Information Sources," "Community Builders," and "Promoters & Mobilizers." The findings suggest that while dialogue is rarely the predominant form of communication, most organizations use dialogue, community-building, and promotion and mobilization in their micro-blogging efforts. The study highlights the importance of understanding the purpose of each tweet and the potential hierarchy of organizational communication functions. The proposed classification scheme is applicable beyond nonprofit organizations and can be extended to other types of organizations and social media platforms. Future research should explore how followers respond to these messages and the interactions between organizations and their constituents.This study examines the Twitter utilization practices of the 100 largest nonprofit organizations in the United States to understand how they use micro-blogging for communication and engagement. The analysis reveals three key functions of micro-blogging updates: "information," "community," and "action." While informational use is extensive, nonprofits are better at using Twitter to engage stakeholders through dialogic and community-building practices compared to traditional websites. The study proposes an "Information-Community-Action" micro-blogging message classification scheme and classifies organizations into three types: "Information Sources," "Community Builders," and "Promoters & Mobilizers." The findings suggest that while dialogue is rarely the predominant form of communication, most organizations use dialogue, community-building, and promotion and mobilization in their micro-blogging efforts. The study highlights the importance of understanding the purpose of each tweet and the potential hierarchy of organizational communication functions. The proposed classification scheme is applicable beyond nonprofit organizations and can be extended to other types of organizations and social media platforms. Future research should explore how followers respond to these messages and the interactions between organizations and their constituents.