Individual interest and self-regulation are two pillars of self-directed learning. Despite empirical evidence on the interaction between the two with respect to academic achievement, few studies have explored how individual interest and self-regulation might interact and relate to self-directed informal learning. This study surveyed 322 university students on self-regulation and two interest constructs (interest in learning English and interest in pursuing personal interest in English), and tested how these factors related to their engagement in self-directed use of technology for English learning beyond the classroom. Structural equation modelling analysis revealed that despite both being significant determinants, interest factors, and self-regulation were associated differently with various types of self-directed technological activities (instruction-, information-, entertainment- and socialization-oriented activities). Self-regulation was predictive of instruction-, information- and socialization-oriented activities, which have high cognitive load and require effort management for second-language learners. Interest in English learning was consistently a significant predictor of all four types of technological activities. Interest in pursuing personal interest in English played a significant role in information- and entertainment-oriented technological activities. The findings recommend greater attention to individual interest when promoting self-directed informal learning. The findings further suggest adopting a differentiated approach to bolstering self-directed learning for different purposes.