This research explores how green social media influencers affect consumers’ electronic word‐of‐mouth behaviour regarding green products by developing cohesive relationships. Grounded in social capital theory and relational cohesion theory, this study aims to understand how green social media influencers can build cohesive relationships with their followers and the subsequent effects of these relationships using a mixed‐method research design. The quantitative study (Study 1) uses a sample of 471 social media users who follow and interact with at least one green social media influencer and employs partial least squares structural equation modelling to analyse the data. The results show that green social media influencers’ cognitive capital and relational capital significantly trigger social interaction frequency, which, in turn, evokes positive mood and reduces uncertainty. This process fosters cohesive relationships and drives electronic word‐of‐mouth behaviour about green products. The study also examines how gender moderates the impact of cognitive and relational capital on social interaction frequency and its subsequent effects on relational cohesion and electronic word‐of‐mouth behaviours. The subsequent qualitative study (Study 2) corroborates the quantitative results and provides complementary findings, enhancing the understanding of how green social media influencers can use their social capital to develop cohesive relationships with consumers and drive electronic word‐of‐mouth behaviours. This research provides significant insights into how green social media influencers can build cohesive relationships with consumers and improve their effectiveness in promoting green products through social capital.