Retailers are adopting 'smart' technologies such as contactless, omni-channel, ubiquitous computing and mobile apps. This paper examines consumer behavior responses while using a mobile instant messaging (MIM) channel adopted by a Chinese pure-play retailer. MIM is text-based, mobile computer-mediated communication technology accomplishing real-time interaction with other users. WeChat, a full service MIM application, contains functional and social features including SMS, LBS, voice message, video calls and "Moments" sharing, which is its social propagating feature. There is a paucity of literature on the role of MIM in building relationships and the relevance of emotion and WOM for consumers engaging in MIM interactions. The model was derived from prior research on Stimuli-Organism-Response (SOR) that depicts the effects of environmental/informational stimuli on consumers' responses. Research objectives included investigating the prediction that environmental stimuli comprising socialness perception, media richness, and involvement induce a positive emotional state, which results in positive WOM. The study employed a quantitative approach. The sample comprised young Chinese WeChat users (n = 486). SEM was used to analyse the data. Prior research has indicated that building relationships with consumers is more difficult when the relationships are consumer-computer as compared to consumer-person. The findings of this study suggest that such a negative effect can be alleviated by the use of MIM. This study is original in integrating socialness perception, media richness and WOM into the SOR framework. The implications for practitioners are discussed, including retailers' need to be aware of the extent to which consumers are willing to engage with MIM applications.