The characteristics of systems-of-systems (SoS) present fundamental challenges regarding properties such as safety, security, reliability, and robustness. This is due to the SoS nature where a collection of independent systems cooperate to fulfil certain high-level objectives. Risk analysis is thus an important activity in SoS engineering. This paper presents a risk analysis method which extends the existing STAMP safety analysis method that is based on systems thinking. Our extensions are aimed at coping with other risks than safety, and the usage is tailored to SoS. The method aims at deriving requirements on the constituent systems that will reduce the emergent risks on the SoS as a whole. The method has been applied to a case study of vehicle platooning.