COVID-19 became a global epidemic after its breakout in December 2019. With the help of information technology, many countries developed contact tracing systems to reduce the spread of the epidemic. Although the WHO declared in May 2023 that COVID-19 is no longer a global public health emergency, the virus is still constantly changing and endangering individuals worldwide. In Taiwan, Social Distancing APP is a voluntary contact tracing app that has been downloaded and utilized approximately 9.5 million times. However, adoption remains low. To prevent the spread of the epidemic and encourage more people to use it, understanding the factors influencing continuance intentions to use social distancing apps is an important topic. The research model is composed of two parts: the modified expectation confirmation model (ECM) and personal norms. Our research model was assessed using data from a sample of 501 users of social distancing apps and was analyzed using the partial least squares structural equation model (PLS-SEM). The results of this study suggest that (1) personal norms are the most important factor influencing continuance intention, followed by satisfaction, perceived usefulness, and descriptive norms; (2) personal norms fully mediate the relationship between injunctive norms and continuance intention; (3) personal norms partially mediate the relationship between descriptive norms and continuance intention; (4) personal norms negatively moderate the relationship between satisfaction and continuance intention; and (5) personal norms positively moderate the relationship between disappointment and continuance intention. This study also discusses the implications of a modified ECM and personal norms for continuance intention to use contact tracing apps.