As social networking service (SNS) platforms become increasingly integrated into foreign language education, their impact on learner motivation and intercultural competence may vary depending on the learning context. This mixed-methods study compares American college students learning Korean as a foreign language (KFL) and Korean learners of English as a foreign language (EFL) to examine how SNS-mediated intercultural contact affects motivational orientations and intercultural development. A total of 107 university students (56 KFL, 51 EFL) engaged in semester-long Facebook-based interactions. Pre- and post-semester surveys assessed intrinsic and extrinsic motivation, intercultural communicative competence, and intercultural sensitivity, followed by qualitative analysis of students’ reflections. KFL learners showed a significant increase in intrinsic motivation across the semester, while extrinsic motivation remained unchanged. Compared with the EFL group, they achieved greater gains in intercultural communicative competence (attitudes and skills) and intercultural sensitivity (respect), reflecting deeper interpersonal engagement and emotional openness. Their reflections emphasized peer-based cultural learning beyond textbook knowledge. EFL learners, without significant motivational changes, showed growth in intercultural communicative competence (knowledge and awareness) and increased confidence and enjoyment in the SNS interaction. Their reflections portrayed the interaction as academically structured and limited in spontaneity. These findings highlight the critical role of learning context in mediating how SNS-based intercultural engagement supports motivation and intercultural development.