How to find out celebrity flight info?

[madison]

Tons of girls I know are able to find out celebrities flight info so they can meet them at the airport. How do they do this?
Don't tell me it isn't possible because it obviously is if these girls are finding out

[Vikky]

they follow 1D update accounts on twitter and maybe have connections, look at the hotel's/airports website, they can find out with other fans, look at their tweets

[Taylor]

make friends with the paparazzi, they'll tell you