Mental illnesses like depression affect 25% of the U.S. population and are the leading cause of ill health worldwide — far above physical illnesses. Chatback is an online emotional support tool that guides peers to use psychotherapy techniques in supportive chats to relieve distress. Chatback differs from prior approaches to online mental health care in scaffolding dialogue, rather than individual reflection in isolation or crowd work in the form of micro tasks. Online chat guidance can help peers to form supportive relationships through deeply insightful chats that promote positive changes in thoughts, feelings, and motivations.