If they are public, no it is not illegal. If they are not public, but I have them because I provide a service to you, then yes it is illegal (most likely). In this case it is public information, and not even personal information. It is a plane identifier and that plane's location. The only reason that tells you anything about it's passenger is because said passenger is rich and entitled enough to own their own plane and use it for themself. It's like buying the Empire State Building to live there by yourself and then complaining about someone tweeting out your address.

https://flightradar24.com

All I need is your flight number. You don't know how any of this works, do you?

You don't even need the Internet, just search up ADS-B receivers on Amazon. The plane and the ATC system itself is tattling on you every second, blasting your position out over the air.

If you put your name, address and phone number on a public forum and someone shares that do you think that's breaking the law? Doxxing generally applies to making personal identifiable information public without that persons consent. Those celebrities are making their own data public, or rather their private jets are because they're required to publicly broadcast their location in real time.

If those accounts are collecting public information they're not doing anything illegal. Otherwise we might as well call libraries illegal because they contain a registry of every book author whose book is in the library.

Source?