In this study, we present a new four-phase crisis model and the development and assessment of a mobile crisis management application. The model development was supported by a participatory process involving Finnish Small and Medium-sized Enterprises (SMEs). The four phases of the model are preparedness, beginning of the crisis, during the crisis, and after the crisis. The new model is incorporated into the mobile app to offer clear, actionable advice for different stages of crisis management. The mobile app, “Crisis Assistant”, is designed to aid SMEs in managing a variety of crises, including infectious diseases, accidents, cyber security threats, personnel issues, and business changes. Recognizing the unique vulnerabilities of SMEs due to their size and resource constraints, and their critical role in the economy, the app aims to provide accessible, user-friendly crisis management guidance. In the mobile app, web analytics provide real-time insights into the content usage, which allows for updates to the crisis guidance content and authorities' instructions as well as the further development of the app. The app has been well-received, highlighting the importance of mobile-based solutions in enhancing SME resilience and preparedness for crises. This study suggests future research should evaluate the app's broader impact on SME crisis management capabilities and applicability to other crisis domains.