This paper investigates the possibility of a scenario-based design approach to increase the efficiency of an existing open innovation platform. This platform shows a great potential for shuffling ideas, but the users report some difficulties in making the design process convergent. From the detailed analysis of a new product design case, we first make a diagnosis of the current platform in order to explain the ill-convergence issue. We then focus on one of the identified weaknesses of the platform: the lack of a shared vision of the needs between the stakeholders, and we propose to improve the existing design process by a new approach based on a scenario-based design framework.