Emerging pervasive technologies such as the Internet of Things and Open Data will have severe impact on the experience, interactions and wellbeing of citizens in future smart cities. Local governments are concerned how to engage and embed citizens in the process of smart city development because without them it is difficult for governments and industrial technology providers to understand what future city is desired. We explore how prototyping methods can be used in a multi-helix approach towards a participatory domain in which multiple stakeholders collaboratively envision a desired future smart city. We adopted the different qualities of generative sessions, hackathons and design jams in our method of participatory prototyping for smart cities. Results show that participants appreciate this setting for exploration, experimentation, and making, in diverse teams with members from industry, government, university, and citizens. We will discuss issues for improvement of participatory prototyping to make it more robust for use in urban development processes.