Since the emergence of e-participation platforms, an increase of public participation has not yet been documented. Recently practitioners and researchers have begun to explore the applicability of gamification in the hope to promote the usage of e-participation services. Gamification has been proven partially successful in several domains, but is only emerging in public participation. This work provides insights on whether game components can promote public participation. We report on the evaluation of a gamified mobile participation application in a field trial that took place in Turku, Finland over a period of five months. We focus on whether specific factors (internal & external) can be used to predict active participation. Our results indicate that citizens are primarily motivated by genuine interest in urban planning. Although gamification had little influence, it did add to some users' motivation. The approach did, however, not succeed in engaging new groups.