The original versions of the USPHS guidelines listed social support as one of the validated behavioral treatments for smoking cessation; however, in the most recent guideline this was dropped because a new meta-analysis concluded that too many of the studies of social support included other treatments that might have caused the improvement rather than the social support (see Westmaas NTR 12:695, 2010 for a review).  In addition, the studies that have tried to manipulate social support to help smokers remain quit have not found consistently positive results.   I think this is because interpersonal support among relatives and friends is so complex, it is hard to manipulate.  Consistent with this buddy systems (that use others in treatment, not friends or relatives) have had somewhat better success.