Absence of ghosts

Hello, I came to ask how do I find ghosts? I have 14 Burial Chambers, and none of them have ghosts, am I doing something wrong?

Update: After searching all day in eight other burial chambers, I found a ghost, which gave me two ectoplasms, and then in four MORE burial chambers, I found another one, which luckily (finally) gave me three ectoplasms, and I was finally able to make my own T.W.I.G.

Looking at the comments, I was really very unlucky.