Throughout the past century, live media has grown to play a significant role in how we experience the world. Live media connects people in real-time with events happening around the world and helps people establish shared social realities. Recent live forms enabled by the internet are shifting the paradigm away from just passively watching to actively participating. This has significant implications for how we engage in critical aspects of society, including education, politics, work, play, and everyday life. In this work, we focus on understanding emerging live media phenomena and designing new forms to support participation. We do this through two core approaches: qualitative investigations and live media probes. To build an understanding of practice and communities, we conduct qualitative investigations of two situated live media contexts: the video game live streaming site Twitch and massive open online courses (MOOCs). Using Marshall McLuhan's concept of hot and cool media, we explore how live streaming as a medium affords building these online communities through participation in shared experiences. Building on these findings, we design, deploy, and evaluate live media probes. These probes implement new forms of live media, with the goal of eliciting new forms of live experience and participation. We first design Rivulet, a live media probe supporting new participatory modalities and multiple simultaneous live streams. Through our investigation of Rivulet, we discover how, by incorporating new modalities, we can support higher-impact forms of participation in live experiences. Next, we design Collaborative Live Media Curation (CLMC), a new live media form enabling the collaborative real-time assemblage of web media including text, images, sketch, and live video and audio. We deploy LiveM?ch?, a CLMC probe, in four situated online learning contexts to support participatory learning activities. We find that CLMC supports new forms of real-time conversational grounding and participation. In conclusion, we summarize and discuss our findings and discuss future directions for live media research.