In the crisis management literature information shared on social media during a crisis is relevant both to emergency agencies, when it establishes a more accurate situational awareness, and to citizens, when it enables a collective and coherent approach to the event (e.g. Stieglitz, Bunker, Mirbabaie & Ehnis, 2018, Journal of Contingencies and Crisis Management, 26(1), 4). Social media is, however, also considered as a place where “noise” and fake news can be dispensed (e.g., Alexander, 2014, Science and Engineering Ethics, 20(3), 717; Starbird, 2017, https://www.aaai.org/ocs/index.php/ICWSM/ICWSM17/paper/view/15603). In this paper, we analyse contributions on Wikipedia and Twitter during major crises in France through online ethnographies and semi‐structured interviews to investigate their roles in building and sharing information. Wikipedia has often been analysed as a collaborative tool but this approach has underestimated its use in reducing uncertainty in times of crisis. We demonstrate that despite their distinct pace and designs, Twitter and Wikipedia are used with seriousness by citizens in their dissemination of information. We also explain how social media change the landscape of means of communication for official institutions and citizens, and that they can be used in the same way. Finally, we stress the need for official institutions to integrate social media in their practices and interactions with citizens that they involve.