Peer feedback is often associated with an increase in the contributions of members in online communities. Verbal feedback (such as a review) can give details about how the recipient can improve their contribution, but it requires the recipient to read and process the feedback. Conversely nonverbal feedback (such as an upvote) is easy to comprehend, but it does not convey much helpful information. Prior studies have mainly focused on the impact of verbal feedback. However, little has been done to explore the underlying mechanism of the effect of nonverbal peer feedback on people’s tendency to contribute more. We present two experimental studies conducted on Amazon Mechanic Turk (mTurkers). Study 1 demonstrates how verbal and nonverbal feedback impact user contributions differently. Next, building on the attribution-emotion-action theory, we use Study 2 to establish a causal mechanism between nonverbal feedback and users’ knowledge contribution. Specifically, users who receive nonverbal peer feedback make internal and external attributions, which in turn impact their emotions and contribution decisions. We find that users receiving more positive feedback attribute this in equal measure internally to perceived self-efficacy and externally to perceived fairness, whereas users who receive negative feedback attribute it more to the lack of perceived fairness of peer feedback. These findings have important implications for both content-sharing platforms and researchers trying to better understand the drivers of online content-sharing behavior.