This paper aims to investigate how social network marketing affects consumers' sustainable purchase behavior (CSPB) while considering the role of Eco-friendly attitude. The statistical population of the study included Iranian users of online social networks with at least one online purchasing experience. An online questionnaire was distributed on Instagram, Telegram, and WhatsApp platforms as the most popular networks in the country. By use of convenience sampling, commonly used in quantitative studies to overcome bias, 450 out of 475 returned questionnaires were acceptable, showing a response rate of 94.7%. The results indicated that an increase in Eco-friendly attitude positively increases the effect of word of mouth on consumers' sustainable purchase behavior. Meanwhile, Necessary Condition Analysis (NCA) revealed that to reach a 50% level of consumers' sustainable purchase behavior, six essential necessary conditions are required: an eco-friendly consumers' attitude at no less than 50%, the trend at no less than 57.1%, word of mouth at no less than 45.5%, interaction at no less than 42.9%, customization at no less than 35.3% and entertainment at no less than 26.7%. Furthermore, the Importance-Performance Matrix Analysis (IPMA) was investigated as a strategic tool. The results of IPMA showed that "buy products that use biodegradable material in packaging", "buy those products that are picked up and recycled", and "buy biodegradable products even if they belong to a less well-known company" show desirable performance and high importance and there is a great opportunity for expansion in this area.
Keywords: SEM-NCA; consumers’ sustainable purchase behavior; eco-friendly attitude; social media marketing activities; social networks marketing.