 This randomized controlled trial tested the effectiveness of an app that encourages individuals to quit smoking with the help of a social network member, Buddy, in daily life. The study found no significant intervention effect on self-reported and SEO-verified daily smoking abstinence at the quit date and three weeks later, but CPD was lower in the intervention group than in the control group. Low app engagement and low perceived usefulness were observed. This article was authored by Phillip Schwaninger, Corina Burley, Hurt Scholes and others.