With the growing interest in and use of online healthcare platforms (OHPs), online medical team (OMT) services have gradually been recognized by physicians as an important multi-channel initiative. However, only a handful of studies have explored the pros and cons of the OMT channel over the traditional individual online service channels in an OHP or examined the critical roles of physicians’ OMT joining behavior. To fill this gap, utilizing two sets of unbalanced panel data, representing high- and low-risk diseases, from 3,500 physicians in a leading OHP in China, we investigate the impacts of physicians’ OMT joining behavior on their online performance based on the trust-transfer theory. The moderating effect of physician’s team involvement is investigated based on data from a famous OHP application. Employing a combination of propensity score matching and difference-in-differences identification, the results indicate that physicians’ OMT joining behavior positively influences their online performance. Furthermore, for the physicians who deal with low-risk diseases, their OMT involvement weakens the positive relationship between their OMT joining behavior and online performance although it has the opposite impact in the case of high-risk diseases. Our subsample analyses provide further insights into how physicians’ OMT joining behavior influences their online performance based on their seniority levels. Specifically, for physicians with higher seniority levels, the team joining behavior positively influences their online performance whereas there is no significant effect for the physicians with lower seniority levels.