||This study addresses the questions of how individuals use social media (SM) to build awareness of social networks (network perceptions) within and beyond SM, and how motivations and SM behaviors differentiate individuals’ ability to build such awareness. The analysis of the 2017 Taiwan Communication Survey (TCS) identifies three types of users based on their motivations for SM use: omnivores, time-killers, and social-groomers, who are differentiated from one another in terms of different types of SM behaviors as well as perceived network structures on SM and beyond. For example, omnivores, who use SM for diverse purposes, tend to engage in SM browsing and reacting more than time-killers, who use SM to pass time. Compared to time-killers, social-groomers, those who use SM for social purposes, are more likely to perceive that they have a larger SM response network, a response network containing close ties, and that they have maintained diverse social relationships in the form of mixed-media relationships (MMRs). Moreover, SM posting is associated with the size and the diverse composition of the perceived response network on SM. More frequent SM posting is also associated with perceptions of having diverse social contacts maintained through MMRs, but such association depends on the size and composition of the perceived SM response network.