Group A: Intervention arm with relapse prevention intervention in the social group via the social networking service (Potential channel: Whatsapp or Facebook). In order to sustain the abstinence among the participants in the social groups, the intervention content is about how to prevent smoking lapse and relapse, how to deal with high-risk situations and facilitate mutual support among participants. Moderators of the social groups will send messages of brief advice, give feedback to participants' enquiries and facilitate conversations in the platform. We propose the moderator to spend about 1 to 2 hours a day for the social group conversation in a flexible time schedule, and the duration will be at least one month. More details about the intervention will be confirmed at the preparation stage.