Nearly all of today's Western teenagers have a profile on a social network site (SNS). As many risks have been reported, researchers and governments have emphasized the role of school education to teach teenagers how to deal safely with SNSs. However, little is known about the specific characteristics which would make interventions effective. Therefore, the overall objective of this research aims to propose a list of validated theoretical design principles for future development of educational materials about risks on SNSs. This research goal was pursued through a design-based research procedure. Thereby targeting teenagers of secondary education in eight separate studies, the different steps of the design-based research procedure have iteratively been completed. Firstly, a problem analysis was executed through three explorative studies, including an observational study, a theoretical evaluation of existing materials and a survey study. Secondly, initial solutions were developed and evaluated in practice through five quasi-experimental intervention studies. Thirdly, we reflected upon all the previous results to produce design principles. Finally, we conclude with an analysis of the design-based research methodology.