Ok, so just to clarify, Photos is an application, not a file. It has a database stored on your system somewhere that holds your images for you. The application Photos can, if you want, look for people for you, too, notwithstanding any key words you may or may not assign. To use that function, open Photos, select "People" on the left column and the resulting display will be of people you have let it identify for you. To add someone to that list, open a photo with them in it and below the picture will be a subset of faces the software has found in the image. Click on one to assign a name. Now Photos will start a process of scanning all of your images to find that face in them. It takes quite a while, as you might expect, for that scanning to complete, so be patient until it finishes. You will see that when you click on People on the left you will see that it is updating and will finish when Photos is in the background. That means leave it running, but click on Photos in the upper left corner and then Hide Photos to put it in the background and let it run. It's not perfect, but it may help you find those images not tagged for whatever reason.