Asking for help for something that is stigmatized but easily hidden from others can be risky. Aspects of online communication channels, such as how anonymous or private someone feels, may make it easier for people to ask for help for these concealable, stigmatized topics. This dissertation tests how people's perceptions of the anonymity and privacy of online communication channels affect how costly they feel it will be to seek support for concealable, stigmatized topics and what they say in their messages. Participants imagined trying to get support for a concealable, stigmatized topic through an online communication channel and wrote the message that they would typically send. Participants rated aspects of their messages, such as the breadth of topics for which they sought support and the emotional content of their message. They also rated their perceptions of the anonymity and privacy of the channel and their perceptions of the costs of seeking support in that channel. Results suggest that people's perceptions of the anonymity and privacy of online communication channels affect how they seek support, such as how often they seek support, the breadth of topics for which they seek support, and the length of their messages. Also, people's perceptions of how anonymous they are in a channel affect their perceptions of the costs of seeking support, which shape aspects of their messages. These findings suggest that people will seek support for concealable, stigmatized topics differently, depending on how they view the channel in which they are communicating. vii TABLE OF CONTENTS LIST OF TABLES .