This study develops a conceptual model to examine determinants of social media adoption for open innovation at the firm level. Building on the technology-organization-environment (TOE) framework, six facilitating conditions are hypothesized to influence a firms` decision to deploy social media technologies for open innovation purposes. Partial least squares (PLS) analysis was used to empirically test our conceptual model on survey data from 120 firms operating in Greece and Cyprus. Outcomes show that large firms are more likely to adopt social media as part of their open innovation strategy, as are firms with a broad external knowledge transfer scope. High competitive intensity, technological dynamism, as well as stringent intellectual property protection regimes tend to positively impact adoption levels of social media.