The rapid spread of social networking and the evolving online environment significantly impact traditional human relationships. As inherently social beings, humans have adapted their relationship-building processes to technological and social changes. With SNS, relationships shift from “maintenance” to “development,” making conventional analyses of “state” and “outcome” insufficient to capture their complexity. This research focuses on the relationship-building process in contemporary communication environments, including SNS, and develops a methodology for analyzing its characteristics in a dynamic and quantitative manner. Specifically, by creating an influence relationship model diagram utilizing the DEMATEL method and visualizing the causal relationships between behavioral elements, the important characteristics and factors in the human relationship formation process were clarified. The research paid particular attention to the characteristics of SNS-use in the youth segment and quantitatively evaluated the degree of influence of the behavioral elements by classifying them into “entry” and “exit” categories. The results suggest that the external factor “reputation from the public” is a key in facilitating relationship building in the online space. Furthermore, it was confirmed that online behavioral elements play a distinct role in relationship building and that their interaction with offline behavioral elements is relatively weak. These findings help organize human relationship characteristics in modern societies and offer practical value for business relationship strategies. The findings provide an important perspective for understanding how the online environment impacts the formation and dynamics of human relationships, as well as thinking about how it can be used for the design of new Internal Communication strategies.