You DO know polyamorous people. People you go/went to school with (maybe one of your instructors), people you work with, neighbors, maybe that police officer you saw the other day, that person in the minivan driving by... they may even be in your own extended family, not wanting to come out to you.
Some people are polyamorous as who they are, even if they're not in a relationship right now or are only with one person right now.
Many polyamorous people are closeted. Some haven't realized they are polyamorous.
I am very happy that polyamory is being depicted more in the media these days.
The potential problem with people unfamiliar with polyamorists seeing a polyamorous relationship depicted in a television show or news story, a talk show, or in a newspaper, magazine, or website article is that they may think, "Ah, now I know exactly what polyamory is like!" That would be like an extraterrestrial watching one fast food advertisement or chef competition television show and saying, "Ah, now I know exactly what meals look like on Earth!" There is so much variety. Media coverage and depictions will have to be increased for more people to get that.
There could be a polyfidelitous family living very close to you, and you don't even know it because they seem like any other average household nearby, just with more than two adults. If there are three adults, perhaps you thought two of them were blood relatives. You could be right, and it could still be a polyamorous home.