A trial of “Making Alcoholics Anonymous Easier” (MAAEZ), a group-format 12-step facilitation program, showed significantly higher odds of past 30-day abstinence after 12 months among those who had been treated in MAAEZ compared to usual care, especially for clients with high prior AA/NA/CA meeting attendance (>90 prior meetings; OR = 2.94, p = .02). We examined whether MAAEZ effects for this group were mediated by social support for sobriety and comfort with the 12-step fellowship. Among those with high prior AA/NA/CA attendance, we performed tests of multiple mediation to estimate MAAEZ effects attributable to the combined effect of social network support for sobriety, comfort being at AA/NA/CA meetings, and comfort speaking at AA/NA/CA meetings. To gain some understanding of sustaining these behaviors, we also examined each potential mediating variable measured both prior to, and concurrent with, 12-month outcomes. Having support for sobriety at 6 months emerged as a mediator of 12-month MAAEZ effects, when controlling for comfort being and speaking at AA/NA/CA meetings at 6 months. The effect remained when controlling for mediator values at 12 months, and explained 44% of the MAAEZ effect. Results highlight the value of studying specific, modifiable 12-step activities, and demonstrate the importance of exploring subgroups to determine behaviors and attitudes to target for optimal treatment. For example, increasing support for sobriety among those with high prior AA/NA/CA attendance may be especially pertinent.