Tumblr is a great platform for creatively promoting your Thunderclap message. It's perfect for sharing images so feel free to choose an eye-catching one that grabs the attention of your audience. While there is no character limit, it's best to keep the writing short and allow your image to be the focus. Tumblr also allows you to post a video or an infographic that may explain your cause better.
Slavery Footprint's Tumblr post included a large detailed image that promoted their Thunderclap campaign.