A hard challenge facing developers of online communities is attaining a critical mass of members and subsequently sustaining their participation. We propose a new mechanism for motivating participation in interest-based online communities, which engages non-contributing members (lurkers) by modeling and visualizing the asymmetrical relations formed when reading, evaluating, or commenting other community members' contributions. The mechanism is based on ideas from open user modeling, a new concept of "community energy," with a mechanism of rating contributions and visualizing the rank of contributions in the community interface.