Volunteers can be a valuable support for disaster management. Disaster management must be able to coordinate volunteers in order to benefit from their support. Interactive, collaborative, and mobile technologies have the potential to overcome the challenges involved in integrating volunteers into crisis and disaster management. This paper presents the ENSURE system, designed to effectively integrate volunteers for an improved approach to disaster management. The system supports the aid forces in recruiting, managing, activating, and coordinating volunteers in the event of a large-scale emergency. To achieve this, ENSURE provides necessary functions such as volunteer registration, volunteer profiles, sending alerts, and volunteer activation (via the mobile app). The system uses a subscription-based approach in which the volunteers agree to take part in an emergency operation by responding to an alert. The system architecture provides technical insights into how to implement crowdtasking systems. It contains seven logical components to provide the necessary features. It was designed to ensure scalability, performance, and availability. The results of a first comprehensive evaluation of ENSURE, which was performed as a large-scale exercise directed by the disaster relief forces in Berlin, were, without exception, positive in all three evaluation areas: efficiency & security, clarity & usability, reliability & availability.