I asked Siri on my Mac "where is X?" and she answered: "X is not on your find my friends list".
Siri can locate this person when I'm using iPhone without any problem. I checked Is there a way to "Find My Friends" from the desktop, rather than iPhone? and I can see the location of this person in Messages app on my Mac. Yet Siri on Mac seems to have a problem with that. Is it a bug or a feature?