The effects of goal interdependence on employees’ performance outcomes have been well documented in the literature. Yet, the relationship between goal interdependence and employees’ proactive behaviors remains largely unexplored. Integrating the theory of cooperation and competition with the employee proactivity literature, this study investigates how cooperative goal interdependence and competitive goal interdependence respectively influence employee knowledge sharing and knowledge hiding, and in turn shape their propensity to seek help from coworkers. It further examines reciprocity beliefs as an individual factor in affecting the indirect effect of goal interdependence on help seeking. Specifically, positive reciprocity belief is hypothesized to moderate the mediating role of knowledge sharing, whereas negative reciprocity belief is expected to moderate the mediating effect of knowledge hiding. In Study 1, a total of 127 interviews were conducted with full-time employees working in professional service firms across four cities including Hong Kong, Macau, China and Taiwan. Results of structural equation modeling supported the mediating role of knowledge sharing in the relationship between cooperative goal interdependence and employee help seeking. In Study 2, an experimental study was conducted with 150 full-time students at a university in Macau to replicate the findings in Study 1 and to test the moderation hypotheses. It yielded findings consistent with Study 1 and supportive of the moderating role of negative reciprocity belief in the mediated effect of goal interdependence on help seeking. Specifically, knowledge hiding mediates the relationship between competitive goal interdependence and help seeking, when an individual is high in negative reciprocity belief. Findings of the two studies provide both theoretical contributions to the literature and practical insights to organizations. Cooperative goal interdependence is a valuable method for managers to promote knowledge sharing, inhibit knowledge hiding, and encourage active help seeking among employees.