Crowdvocate.org is our platform for crowdsourced messaging. Crowdvocate helps with exploratory message development, by hosting tournaments where diverse users compete to write novel and high-impact messages. To sponsor a tournament, an organization defines the target audience and outcome (e.g. attitude or belief), and then our panel of hundreds of users attempt to design the most impactful message for moving the outcome. We efficiently test the messages using adaptive randomized experiments, award prizes to the winning users, and share all results with the sponsoring organization.