Engagement platforms (EPs) are an essential technology to enable modern co-creation and service innovation. Therefore, the design of these platforms is receiving increasing attention in research. In this study, we thus conducted expert interviews with founders, CEOs, and managers of 14 personal and household-related service platform companies from the DACH region, to gain insights into their activities and mechanisms for creating and maintaining successful EPs. Drawing from a preceding literature analysis, we offer a categorization according to the four categories: easing the entry, identifying mutual needs and problems, supporting co-creation, and facilitating service innovation. In addition, the data analysis found that the measures and activities carried out by platform owners are motivated by three concepts: trust, commitment and visibility. Overall, 29 mechanisms were identified, which aid in designing EPs. Thereby, both scholars and practitioners are presented with actionable knowledge to advance their EP endeavors.