Live streaming is a unique medium that merges different layers of communication by facilitating individual, group, and mass communication simultaneously. Streamers who broadcast themselves on live streaming platforms such as Twitch are their own media entity and have the challenge of having to manage interactions with many different types of online audiences beyond the translucent platform interfaces. Through qualitative interviews with 25 Twitch streamers, in this paper we share streamers' practices of discovering audience composition, categorizing audience groups, and developing appropriate mechanisms to interact with them despite geographical, technological, and temporal limitations. We discuss streamers' appropriation of real-time signals provided by these platforms as sources of information, and their dependence on both technology and voluntary human labor to scale their media entity. We conclude with design recommendations for streaming platforms to provide streamer-centric tools for audience management, especially for knowledge discovery and growth management.