The continuing rise of online retail comes at the expense of small and medium-sized stores in local high streets. Many cities now experience substantial vacancies and the decline of independent and family-owned stores, impeding citizens’ perceived quality of living. In this paper, we design the community platform ‘smartmarket²’, with which networks of local retailers interact with networks of customers to co-create a physical and at the same time digital customer experience in a high street. The platform connects with retailers’ information systems, while interfacing with in-store technologies to connect with potential customers’ smartphones. From a theoretical perspective, the platform exemplifies how previous research on value co-creation, multi-sided (engagement) platforms, and retail communities can complement each other to constitute online-offline customer experience. Based on comparing smartmarket² with rival IT artifacts, we abstract nascent design knowledge by conceptualizing a design theory for ‘community platforms for high street retail’ as a new class of IT artifacts. We conclude the paper with identifying how digital services—including cross-promotions, geographical recommender systems, and geospatial analytics—may be offered on the platform to leverage the competitive position of small and medium-sized retailers in local high streets through online-offline customer experience.