This is the best discussion I can find on the subject. Apparently a Warlock with pact of the chain can communicate with their familiar as long as it is on the same plane of existence.

https://rpg.stackexchange.com/questions/76171/can-a-familiar-travel-any-distance

Most other classes (Sorceror and Wizard for the most part) can communicate telepathically out to 100', or empathically out to 1 mile. That said, there's no maximum distance that a familiar can travel from it's master, it just won't be able to instantly communicate.