Sticker use is an increasingly popular part of daily messaging activity. However, little is known regarding the types, functions, and outcomes of sticker use in authentic online communications. To investigate these phenomena, we analysed sticker use in five small mobile-messaging-facilitated discussion groups initiated by students for course projects in an Asian university. The students used four types of stickers, among which ‘animated picture without text’ was the most frequent. Sticker functions fell into two main categories: as a tone indicator with scope over a textual message, and as a stand-alone illocutionary act. Based on interviews with seven participants, we found disparities between the sender’s intention and the receiver’s interpretation for 34.7% of the stickers, but these disparities did not adversely affect the communication. Implications of the findings are discussed.