It's common knowledge that the paparazzi usually follow celebrity news. Before they start to stalk their favorite celebrities, they might have done some research. The paparazzi have personal assistants that collect the information and relay the relevant details to the paparazzi.
One of the best ways to stalk celebrities is by keeping track of their movements through their travel plans. For instance, when a celebrity books a flight, their movements are made public. They also post pictures of their plane ticket online.
They can be easily tracked as soon as they land. The paparazzi then hire a taxi or a private car to follow the celebrity. They rely on the media to keep them updated with information on a celebrity's travel plans.
Paparazzi have lots of contacts and friends. They have the ability to get hold of your flight schedule before you do. So the only way to fight back and protect your privacy, is to book the flight under a fake name.