Run User Portal Report
In application links, Click on "Portal Reports"
Once there, you will select the drop down arrow, and then choose "Portal Users".
Click the Blue/White Icon.
Once Loaded, click the binoculars in the top right. You will get a pop-up.
Enter the name, and click find next. This will highlight the information in blue. Click Find next multiple times to determine all portals the person is on.