How should digital platforms engage with and invest in their online communities to shape innovation and knowledge contributions from members in their platform ecosystems? This is an important question because user contributions are important drivers of technological progress and business value. We examine the effect of platform sponsors’ investments in online communities on user knowledge contributions, using fine-grained longitudinal data from a leading enterprise software vendor’s community network. We focus on the sponsor practice of knowledge seeding, in which its employees provide free technical support by answering questions posted in discussion forums. We define user knowledge contribution as peer-evaluated, quality-weighted solutions that community members provide to help resolve the questions their peers raise. We show that the platform sponsor’s investments in knowledge seeding have a positive, significant association with user knowledge contribution. We also find temporal and geographical variations in returns on the sponsor’s knowledge investments. Specifically, returns (i.e., amount of user contribution that is stimulated) decrease with the age of the community, consistent with the observation that the most active contributors are lead users who tend to join the community early. In addition, returns vary across different countries, such that greater returns are realized when the investment is made in countries with higher levels of information technology (IT) infrastructure, partly because country-level IT infrastructure may be associated with greater absorptive capacity of these countries. We discuss the implications for research and practice.