A lot of people said they didn't understand this concept, which I found frustrating. Unless you are the kid from "Room" (2015), at some point in your life you learned that there were people in the world that you don't know but that people that you know know.
I get that people got hung up on how it would work, but that wasn't the question.
Anyway, I don't think Friends of Friends is a concept beyond mortal ken.