As a special type of social information systems, crowdfunding platforms draw researchers' attention in recent years for their increasing popularity. In supplement to big-data analyses on usergenerated content, behavioral research using survey and interview observations provide insights on why people like or hesitate to use such platforms. Nevertheless, extant studies focus on user intention and equity/reward-based projects, leaving the knowledge body on why people actually engage in donation-based crowdfunding underdeveloped. Based on Activity Theory, this study explores the critical success factors of crowdfunding in terms of website acceptance, crowd familiarity, and donation reciprocity. It then develops a research model that adapts relevant constructs from e-commerce and charitable behavior literature to predict user trust and readiness leading to actual donation. To test the hypothesized relationships, a structural equation modeling analysis was performed on 744 survey responses collected from crowdfunding platform users in multiple countries. Results provide supporting evidence to most hypotheses and confirm the importance of factors related to the technological system as well as social collaboration in the crowdfunding activity.