Research has shown that many people use social networking sites (SNS) excessively, which may lead to various negative consequences. With the aim of reducing SNS addition, this study investigates the role of SNS characteristics in the formation of SNS addiction. By applying incentive sensitization theory in the context of SNS addiction, we suggest that the compulsive motivation for using an SNS is developed by pleasurable and rewarding SNS use experiences. Social network characteristics and communication characteristics, which determine the rewards that users obtain from SNS use, moderate the relationship between habitual SNS use and SNS addiction. We develop novel behavioral measures of habitual SNS use and SNS addiction based on SNS activity logs and empirically test the research model using a large and unique dataset. Besides contributing to the theoretical development of SNS addiction, the results of this study offer practical options to help prevent SNS addiction. Moreover, the measures of SNS addiction enable the automated monitoring of user behavior on SNS, which could be useful for detecting potential SNS addicts