Since watching movies is a social experience for most people, it is important to know how an application should be designed for enabling shared cinematic virtual reality (CVR) experiences via head-mounted displays (HMDs). Viewers can feel isolated when watching omnidirectional movies with HMDs. Even if they are watching the movie simultaneously, they do not automatically see the same field of view, since they can freely choose their viewing direction. Our goal is to explore interaction techniques to efficiently support social viewing and to improve social movie experiences in CVR. Based on the literature review and insights from earlier work, we identify seven challenges that need to be addressed: communication, field-of-view (FoV) awareness, togetherness, accessibility, interaction techniques, synchronization, and multiuser environments. We investigate four aspects (voice chat, sending emotion states, FoV indication, and video chat) to address some of the challenges and report the results of four user studies. Finally, we present and discuss a design space for CVR social movie applications and highlight directions for future work.