Confronting the dual challenges of diminishing traffic dividends in social media advertising and weakening user engagement, enterprises are increasingly adopting value-driven advertising strategies. According to Quest Mobile statistics (2024), CSR marketing in the cosmetics industry has risen to become the sixth most prevalent marketing strategy. However, significant disparities exist in actual conversion effectiveness, making the optimization of CSR strategies to enhance advertising engagement crucial for marketing breakthroughs. Guided by the heuristic-systematic dual-process theory, this study explored how CSR fit influenced consumers' engagement intentions with social media advertising and how this relationship was mediated by brand trust and moderated by message specificity. Through a 2 (CSR fit: high vs. low) × 2 (message specificity: abstract vs. concrete) between-subjects experimental design (N=316), the theoretical framework was validated using structural equation modeling. The key findings revealed that: (1) CSR fit positively influenced social media advertising engagement intentions through the full mediation of brand trust, demonstrating a sequential 'high fit-high trust-high engagement' pathway. Engagement intentions in the high-fit condition were significantly higher than those in the low-fit condition ("M_high = 6.14 vs. M_low = 4.82, p < 0.01"); (2) Message specificity moderated the impact of CSR fit on brand trust. High CSR fit generated greater brand trust than low fit under concrete information conditions, whereas high fit paradoxically reduced trust in abstract information contexts. This research elucidates the synergistic mechanism between CSR fit and message specificity in CSR communication, providing theoretical foundations for optimizing CSR marketing strategies in the new media landscape. The findings offer practical insights for enterprises to enhance advertising effectiveness through strategic alignment of CSR initiatives and information design.

CSR Fit, Consumer Engagement, Brand Trust, Message Specificity, Social Media Advertising