Is it possible to hang something on the wall surrounding my chimney?
I would drill a small hole through the plaster first to test your theory about how much space you have behind the plaster.  Your bit will stop when it hits the chimney, and you can use that to judge how much room you have.

If you have enough room, I would go with a toggle bolt style fastener.  If not, then you might need to use a masonry bit and drill into the chimney.  From there you can use a long tapcon screw to go through the plaster and into the chimney brick.