To influence user behaviors, Internet-based virtual humans (VH) have been used to deliver health interventions. However, Internet-based VH health interventions face challenges. The challenges can affect user perceptions of an Internet-based VH health intervention. In our work, we use an Internet-based VH health intervention to promote colorectal cancer (CRC) screening. We present design guidelines drawn from two studies. The two studies examined the influence of visual design and the influence of the information medium on user intentions to pursue more health information. In the first study, the analysis of the focus group (n=73 users) transcripts shows that the VH\'s visual realism, the VH\'s healthcare role, and the presence of a local healthcare provider\'s logo influenced user perceptions of the VH-based intervention\'s visual design. The findings from the focus groups were used to iterate the intervention and derive design guidelines. In the second study (n=1,400), the analysis of online surveys of users after the VH-based intervention showed that very few users focused on the VH\'s appearance. To influence the user intentions to pursue the health topic further, the results recommend the use of an animated VH to deliver health information compared to other mediums of information delivery, such as text. The design guidelines from the two studies can be used by developers to use VH-based interventions to influence users\' intention to change behaviors.