The use of social network service (SNS) applications for health communication has revolutionized communication between physicians in recent years. We performed an unrestricted retrospective study focusing on emergency physicians (EPs) in Kyoto University Hospital (KUHP) since timely communication is important during emergencies. EPs used LINE, a popular SNS application in Japan. EPs (n = 22) sent 1752 messages from April 2017 to March 2018. Most messages sent contained text data (82.1%), the remaining contained media (17.9%); media included images (72.6%), LINE stamps (22.9%), LINE albums (2.3%) and files (1.6%). Content analysis by two coders produced 13 categories (n = 1438); these were ‘miscellaneous’, ‘patient’, ‘team’, ‘treatment’, ‘event’, ‘situation’, ‘reference’, ‘announcement’, ‘schedule’, ‘resource’, ‘policy’, ‘transport’ and ‘unknown’. The top five message categories were related to miscellaneous chat (22.5%), patient (19.1%), team (14.3%), treatment (11.8%) and event (6.6%). The largest number of messages among EPs were sent on Monday and Friday. The numbers of messages sent among EPs during day-shift and night-shift were similar. The categories identified influenced our proposal of medical oriented SNS platform features: structured tagging system for messages related to relevant categories (F1); inquiry broadcast system for specific inquiries using structured tagging (F2); image tagging system for images shared within groups (F3) and summarized notifications (F4). Features that need consideration are (1) an opt-in location sharing system between physicians and (2) physicians’ access to patient records from the SNS application. In this study, messages discussed by EPs were categorized and the resulting categories influenced our proposal of a physician-centered SNS platform customized to EPs’ roles. Since physicians prefer using SNS applications compared to traditional mobile phones, their information needs should be considered. Designing a medical oriented SNS platform that is physician-centered should first include an understanding of topics discussed by physicians. Based on the categories classified, the proposal of physician-centered features for designing a medical oriented SNS platform is also discussed in this paper.