Human Computation Games (HCGs) harness human intelligence to tackle computational problems. As in any game, a fundamental mechanism in a HCG is its reward system. In this paper, we investigate how virtual reward systems evoke perceptions of enjoyment in HCGs. Three mobile applications for location-based content sharing (named Track, Badge and Share) were developed for an experimental study. The Track version offered a points-based reward system for actions such as contribution of content. The Badge version offered different badges for collection while the Share version served as a control which did not have any virtual reward system. The experiment had a counterbalanced, within-subjects design. For each application, participants performed a series of tasks after which a questionnaire survey was administered. Results showed the Track and Badge applications were perceived to have more accurate and complete content than the control (Share) application. Further, participants reported being more engaged when using the former two applications.