This paper highlights some of the difficulties experienced by volunteers and members of the general public when coordinating a response to an emergency in Pakistan, and discusses a participatory approach to investigating the requirements of an online emergency response platform that links volunteers with donors. The approach builds upon the use of a prototype platform in a simulated emergency situation with real users to test assumptions and learn about the design requirements for such a platform. The paper details the design process and the features of the prototype, and the feedback it received from users.