My classmates non classmates ghosted from facebook

It is 10.45 am. I'm sitting in class waiting for the professor to arrive. A few of my classmates are here as well. I can see 2 friends from my facebook feed. Why are they not here?<br><br>I checked the students lists of various universities, the city website, people search engines. I couldn't find them. They non exist. I saw them twice this semester. I am stumped.