In this multi-platform, comparative study, we analyze social media messages from political candidates (N = 1,517) running for Congress during the 2022 U.S. Midterm election. We collect data from seven social media platforms: Facebook, Twitter, Truth Social, Gettr, Instagram, YouTube, and Rumble over the 4 weeks before and after election day. With this unique dataset of posts, we apply computational methods to identify messages that sought to mobilize individuals (online and offline) to donate money, vote, attend events, engage with the campaign online, and visit the campaign’s content on other platforms. We find that Democrats were not on alt-tech platforms in 2022 and that both Republicans and Democrats use video-based platforms for multiple mobilization strategies. Mobilization messages varied for House and Senate candidates of both parties across platforms, before and after election day.