Simple Summary: This study assessed the relationship between pet ownership, pet attachment, loneliness, and coping with stress before and during the COVID-19 pandemic . Contrary to our hypotheses, results did not support the presence of a buffering effect of pet ownership on loneliness, with pet ownership predicting increases in loneliness from pre-pandemic to during the pandemic . Dog owners showed lower levels of loneliness prior to the pandemic as well as higher levels of attachment, suggesting possible species-level differences in these relationships . Pet owners also reported spending time with their pet as a highly used strategy for coping with stress, suggesting that future research should explore the role of pets in coping with stress and social isolation during the pandemic . These results indicate that the relationship between pet ownership and adolescent loneliness during the pandemic is complex and warrants further research . Abstract: The pandemic associated with the emergence of the novel coronavirus (COVID-19) is an unprecedented historical event with the potential to significantly impact adolescent loneliness . This study aimed to explore the role of companion animals and attachment to pets in the context of the pandemic . We used longitudinal quantitative survey data collected prior to and during the pandemic to assess the role of pets in predicting adolescent loneliness . Pet ownership was not a significant predictor of loneliness before the pandemic, but did predict higher levels of loneliness during COVID-19 as well as higher increases in loneliness from before to during the pandemic . Dog ownership predicted lower levels of loneliness prior to, but not during the pandemic, and dog owners were significantly more attached to their pets than non-dog pet owners . Adolescents with pets reported spending more time with their pets during the pandemic, and frequently reported pet interactions as a strategy for coping with stress . Overall, the results from this study did not support the presence of a buffering effect of companion animals on loneliness for adolescents and indicate complexity in the relationships between pet ownership, attachment, loneliness, and coping with stress . These results suggest a need for additional research further assessing how features of the relationship such as species and relationship quality might contribute to adolescent mental health outcomes.