Coming out and being visible online can offer transgender and/or non-binary people benefits not found elsewhere. However, it also can expose them to negative reactions and bad experiences. Through an analysis of 15 semi-structured interviews, we investigate the experiences of transgender and/or non-binary people coming out across social media sites (SMSs). We found that participants employed strategies around disclosure and visibility to limit the consequences of coming out and to access support. Using trans theory on visibility, we discuss how online spaces present metaphorical "doors" to resources, support, and recognition---but can also be "traps" for those that do not meet the expectations of the space. We discuss how visibility empowered participants to create "trapdoors" to new spaces within SMSs where they could create positive outcomes for themselves and their communities. We close with considerations for designers as they create online spaces, and present a broader call to action for the HCI community around designing online spaces.