Although various scales have been developed with the aim of measuring students' social anxiety in a variety of settings, none of the studies has addressed the measurement of social anxiety in social media platforms. This study describes the process of developing and validating a multidimensional Social Anxiety Scale for Social Media Users (SAS-SMU) that can be used to assess college students' social anxiety arising from social media platforms. The study was conducted in two phases. In the first phase, data collected from 174 students were used to provide evidence for validity and reliability of the structure and its underlying dimensions. A four-dimensional structure emerged: shared content anxiety, privacy concern anxiety, interaction anxiety, and self-evaluation anxiety. In the second phase, data collected from 510 college students were used to confirm four-factor structure of the 21-item SAS-SMU. The Cronbach's Alpha coefficients for the dimensions ranged from 0.80 to 0.92, demonstrating a satisfactory level of reliability. Further validation studies were also conducted and their findings provided. This validated scale will be a useful tool for both researchers and instructors to assess college students' social anxiety as social media users. (C) 2017 Elsevier Ltd. All rights reserved.