In recent years, people have witnessed the growing popularity of mobile health applications, which represents a promising solution for health management. Developers of such mobile apps routinely deploy incentive programs, in which users receive financial rewards after achieving certain performance goals. In this paper, we seek to identify the effects of financial incentives, and to take a close examination at strategic behavior of users who self-report their performance. Drawing on the behavioral economics literature on incentives, we leverage a field quasi-experiment on a mobile health application to identify the effect of financial incentives. Using a difference-in-differences framework, we find that financial rewards lead to improvements in weight loss performance during the intervention period compared to the control group without financial rewards, but the performance difference does not persist after the removal of financial rewards at the end of the intervention period (i.e. no post-intervention effect). More importantly, we find evidence of strategic behavior: participants tend to over-report their initial body weight so as to increase the likelihood to reach performance goals and obtain the rewards. Further, we find that certain social networking features could possibly mitigate strategic behavior. In particular, participants who have more social connections and social activities are less likely to behave strategically. Our study contributes to the IS literature on leveraging economic incentives for online behavioral interventions and provides insights for the implementation of such incentives on digital health management platforms.