For VFR (visual flight rules) flights in the U.S., a flight plan is not needed and many such flights are made without a flight plan. If a VFR flight is conducted without talking to anyone, to and from uncontrolled fields, then they would be squawking 1200, in which case the flight wouldn't be identified on Flight Aware. Unless there's some unique ID being transmitted by ADS-B...
I have a great story from my friend's father when we were kids in the western US. They lived at one of these residential airstrip developments, and owned a remote ranch about 60 min. away by air. The father was in the habit of commuting between his home and ranch at will.
Flying home one day he found himself flanked by two fighter jets and escorted to the nearest commercial airport. He was hustled into the back of a black SUV and taken to his home where is family was gathered in the living room giving statements to a bunch of men in suits. Turns out the POTUS was is town for a visit, and my friends father had failed to read the temporary flight restriction advisory..
> they would be squawking 1200, in which case the flight wouldn't be identified on Flight Aware
My 1200 flights frequently show up on FlightAware, FYI.