In this article, I will analyze the ways in which Brazilian workers are using social media to organize and mobilize. Although analysis of social media use has made great progress, in the case of worker movements it still needs further development. I will focus on the experience of Brazilian app-based delivery workers during the COVID-19 pandemic. Despite their dispersion across the country, delivery workers were able to carry out two national strikes through intense use of WhatsApp, Facebook, YouTube and Twitter. Using qualitative analysis of posts from worker organizations on social media, it was possible to identify the challenges faced by these movements when using digital media. Social media helped solve some organizational and communication problems, while producing others that workers had to deal with. In this article, I will analyze the ways in which Brazilian workers are using social media to organize and mobilize. I will focus on the experience of Brazilian app-based delivery workers during the COVID-19 pandemic. My research was carried out throughout July 2020, when the workers went on strike for higher pay and better working conditions. I employed a qualitative methodology of observing, selecting and analyzing about five hundred social media posts by delivery workers and their unions, associations and independent collectives. To organize the strike, they most often used Facebook, YouTube, WhatsApp, Twitter and Instagram. I thus focused on these platforms while collecting text, audio and video posts. I also obtained empirical data through monitoring and direct observation of the movement in the streets, as well as through interviews with delivery workers. The results indicate that the movement succeeded in expanding and disseminating its influence among and beyond delivery workers through the complementary use of online and offline actions. The movement thus gained more visibility and was better able to organize spatially dispersed workers. Engagement and participation were ensured through the use of networks, which thus played a prominent role in helping build and disseminate a collective identity, and which then became a means to undertake political action. Despite their gains, delivery workers also encountered formidable challenges. Their greater visibility increased the ability of companies to identify and repress movement organizers. In addition, internal fragmentation was not overcome, either offline or online. Although these movements owe their strength to social media, digital organization alone cannot solve their political or organizational problems. Keywords: delivery workers; workers' digital action; digital platforms; collective action; Brazil L'article analyse comment les travailleurs bresiliens utilisent les reseaux sociaux pour leur organisation. En suivant les reseaux sociaux des organisations des travailleurs, nous avons verifie les defis apportes par ce nouvel instrument dans l'action collective. L'analyse porte sur la mobilisation des livreurs de plateformes, realisee tout au long du mois de juillet 2020, lors de la pandemie de COVID-19 au Bresil. La recherche utilise une methodologie qualitative en observant, selectionnant et analysant environ cinq cents publications sur les medias sociaux de ce groupe professionnel. Les medias sociaux les plus utilises tout au long du processus d'organisation de la greve ont ete Facebook, Youtube, Whatsapp, Twitter et Instagram. Ainsi, la recherche s'est concentree sur ces medias, collectant des publications au format texte, audio et video. De plus, des donnees empiriques ont ete obtenues par le suivi et l'observation directe des deplacements dans les rues, ainsi que par des entretiens avec les participants. La recherche indique que les usages complementaires entre les actions en ligne et hors ligne, le succes dans l'expansion et la diffusion du mouvement a l'interieur et a l'exterieur du groupe professionnel, lui donnant une grande visibilite, l'aide a l'organisation d'un groupe professionnel disperse dans l'espace garantissant l'engagement, l'utilisation des reseaux a joue un role preponderant dans la construction d'une identite collective desormais reconvertie dans l'action politique en tant que sujet politique collectif. Malgre tous ces gains, les defis etaient egalement de taille. Par exemple, la visibilite a augmente la capacite des entreprises a reprimer les participants et la fragmentation organisationnelle interne du groupe n'a pas ete surmontee hors ligne ou en ligne. Tout cela indique qu'aujourd'hui, malgre le fait qu'il est impossible de penser ces mouvements sans recourir aux reseaux sociaux, il ne faut pas penser qu'ils peuvent a eux seuls resoudre les problemes politiques et d'organisation. Mots-cles: Livreurs; Mobilisation en ligne des travailleurs; Plateformes numeriques; Action collective; Bresil, 1. Introduction In this article, I will analyze the ways in which Brazilian working-class movements are using social media in their struggles, my aim being to identify the challenges this [...]