Online engagement is key to sustaining online connective action over time. However, there is limited research on how social media messages can trigger diverse connective actions, quantifying more precisely the different forms of online engagement generated with social protest, especially those related with environment and climate change. To this end, this study analyses a random sample of tweets containing #fridaysforfuture to identify which message characteristics motivate people to engage online in the digitally networked action against climate change. Results evidence that depends on who send messages (Greta Thunberg and icon-influencers), what content (“not supporting the movement” and “information about COVID-19 and digital strikes”), when (during business hours), and how (audiovisual format and other hashtags), higher levels of online engagement with #fridaysforfuture are generated via retweets, cited tweets, likes, comments, and replies to comments. This study contributes to previous literature expanding the empirical applications of the connective action theory, using a broader and deeper metric of online engagement with social movements, and providing a bigger picture on the debate on the importance of message strategies to generate higher engagement with social protest. This research offers implications to optimize message design, fine-tune communication strategy in general, and, in the case of social movements, to reinforce digitally networked action.