Quite frequently, I use the az command-line tool to explore my Azure resources. Sometimes, I want to use the GUI (aka the Azure portal) when I'm trying to manage several resources at the same time.
I discovered that if I search for a service principal by name in the Azure portal, it doesn't show up as a resource. To find the principals, instead, search for the Azure Active Directory service.
From Azure Active Directory pane, click on App registrations.
From that pane, I can choose to see All Applications or Owned Applications.
The term Application here isn't implying that it's an actual application. Instead, these are components that are associated with applications. In this case, the App registration pane shows all Application objects and Service Principals. From here, it's possible to search for a specific service principal.
For more quick real-world scenarios on Azure, check out the Azure Tips and Tricks site.