I am so sorry, I would be horrified, worried and angry. I hope you find your bulldog but in the meantime, get the cameras up and put padlocks on every cage, crate, door and etc so they can only be opened with a key...take pictures of each one for later documentation (time and date stamped if possible) and if someone comes to let someone out, they will have to cut the lock away....predators of the 4 legged variety do not carry bolt cutters so that should get the police hopping. Also, contact the local human society or TV station, tell them about it, start making waves and get some attention brought to it, maybe that in and of itself will stop the criminals...they are criminals to do something like this...they are harming and endangering pets.
And prosecute to the fullest extent of the law if you can catch someone on the cameras or in the act. Put them in jail and feel no sympathy doing it regardless of age or otherwise...lock them up because they need help.
Good luck to you and My heart is with you, I pray no other animals are the victim of this criminal or criminals. Also, invest in 50lbs of flour. Cover the ground in front of every cage, gate, door and window and look for prints.