Given the rising popularity of social networking sites (SNSs), the influence of these platforms on the subjective well-being (SWB) of their users is an emerging topic in information systems research. Building on the norm of reciprocity and the social functional approach to positive emotions, we posit that targeted reciprocity-evoking forms of SNS activities are best suited to promote users' positive emotions. The favourable potential of these activities is likely to be particularly pronounced among adolescents who pay special attention to social acceptance, which can be channelled with the help of reciprocal communication. Therefore, we conducted a quantitative 7-day diary study of 162 adolescent Facebook users attending German schools, looking at the impact of their daily SNS activities on their SWB. Based on a linear mixed model analysis, our results confirm a positive link between targeted reciprocity-evoking activities - such as chatting, giving and receiving feedback - and adolescents' positive emotions. Our findings provide a reassuring perspective on the implications of the sociotechnical design of SNS communication channels. Specifically, by encouraging targeted activities, providers, users, and other stakeholders can ensure the beneficial impact of this technology on users' SWB.