Study: NCT03992742

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Initial phase: personalized instant messaging (PIM)
Description: intervention Group participants will receive three months of personalized interaction through IM Apps (e.g. WhatsApp, WeChat). Our counsellors will trigger the conversation and encourage the participants to set a quit day. A total of pre-set 26 messages will be sent with the schedule of once daily for 1 week (the week across the quit date), 3 times a week for 4 weeks (2 weeks each before and after the week with quit date) and once a week for remaining 7 weeks. These messages covered generic information about the benefits of quitting, methods to avoid/ manage craving or withdrawal symptoms, and encouragement to quit and use SC services.~At the end of the initial phase (1-month), complete responders (quitters) will continue to receive PIM (subgroup C). Incomplete responders (smokers) will be randomized to continue PIM (subgroup B) or receive OCI (subgroup A).

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Second phase: optional cocktail interventions (OCI)
Description: For incomplete respondents (subgroup A) randomized to OCI, the available intervention options include multi-media messages, active referral plus financial incentive, phone counseling, family/peer support and medications (NRT). Participants will be guided by cessation counsellors at 1-month follow-up telephone survey to choose any combination of OCI based on their preference. If OCI participants cannot be followed up at 1-month, they will receive multi-media messages by default.

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Initial phase: regular instant messaging (RIM)
Description: Participants enrolled in the Control Group will receive regular messages via IM services (e.g. WhatsApp, WeChat) since initial contact and until 3-month after baseline with a tapering schedule: 1) Baseline to 4-week (1-month): 2 times/ week (8 in total); 2) 4-week to 12-week (2- \& 3-month): 1 time/week (8 in total).~SC messages will generally include benefits of SC, encouragement on abstinence and use of SC services, tips on avoiding/ handling craving and reminder of participating in telephone follow-up. A reminder to participate in the telephone follow-up will also be sent at 1-, 2-, 3- and 6-month, making up a total of 20 messages.~At the end of the initial phase (1-month), complete responders (quitters) will continue to receive RIM (subgroup F). Incomplete responders (smokers) will be second randomized to continue RIM (subgroup E) or receive PIM (subgroup D). Those who are unable to follow up at 1-month will be considered as nonresponsive to the intervention.

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Second phase: personalized instant messaging (PIM)
Description: For incomplete responders allocated to PIM (subgroup D), participants will receive the same intervention as the Group A delivered at the initial stage. Participants will receive two months of personalized interaction through IM application. Please refer to Intervention Group Initial phase: personalized instant messaging (PIM) for details.

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: AWARD advice
Description: Ask about smoking history, Warn about the high risk of smoking, Advise to quit as soon as possible, Refer to the smoking cessation services, and Do it again (if the smokers refused to set quit date).

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: AWARD advice
Description: Ask about smoking history, Warn about the high risk of smoking, Advise to quit as soon as possible, Refer to the smoking cessation services, and Do it again (if the smokers refused to set quit date).

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Warning leaflet
Description: The 2-sided color printed A4 leaflet, which systematically covers the most important messages to motivate smoking cessation

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Warning leaflet
Description: The 2-sided color printed A4 leaflet, which systematically covers the most important messages to motivate smoking cessation

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Referral card
Description: The 3-folded Smoking Cessation Services card consists of brief information and highlights of existing smoking cessation services, contact methods, motivation information and strong supporting messages or slogans

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: Referral card
Description: The 3-folded Smoking Cessation Services card consists of brief information and highlights of existing smoking cessation services, contact methods, motivation information and strong supporting messages or slogans

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: COSH booklet
Description: A general smoking cessation self-help booklet

Intervention type: BEHAVIORAL
Group type: EXPERIMENTAL
Intervention: COSH booklet
Description: A general smoking cessation self-help booklet