Background: During the COVID-19 pandemic, social media became an important and easily accessible source of information to keep the population informed. In this study, we explored how Portuguese health entities used social media during the public health emergency caused by COVID-19 disease. Methods: A retrospective study on Portuguese public health entities’ communication with the public using social media platforms was performed. Data were retrieved from Facebook, Instagram, and Twitter. All retrieved posts were analyzed, and the engagement of the public was calculated. A thematic analysis of all COVID-19-related posts was conducted. Results: The analysis of each social media platform revealed that during the COVID-19 pandemic, health entities reinforced their presence on social media platforms. The most published posts were related to “epidemiological context” and “encouragement to take actions” to avoid the spread of COVID-19. High engagement frames were not associated with the most frequently published posts. Conclusions: Although health entities have reinforced their presence on social media platforms, they do not take full advantage of these platforms to improve health literacy.