This study aims to evaluate the moderating role of social media influence before and after the trip in Vietnam and Czech Republic. Primary data, gathered during time lag data surveys conducted among international tourists travelling to the Czech Republic and Vietnam, was analyzed with the Structural Equation Modelling (SEM) in R. The findings revealed that social media influence with higher level positively strengthened the connection between tourist motivation and the post trip destination image. Furthermore, social media had a significant moderating effect on the relationship between tourist satisfaction and ecotourism loyalty. However, there are strong differences between the destinations of developed and emerging economies. For Czech Republic, as developed economy, social media influence plays a more important role as a value-expressive mechanism at the post-trip stage whereas for the developing economy of Vietnam, social media plays a more important role as an information source before the trip. This study extends the Expectation Confirmation Theory (ECT) by introducing the moderating effect of social media influence, which first time measures this moderating effect before and after the trip accounting for the dynamic nature of the destination image as an antecedent of ecotourism loyalty. Limitations, theoretical implications, and recommendations for practice and further research are addressed. JEL Classification: L83, Z30, Z39