you can sleep(very short intervals)at near the spot where the shield got stolen. eventually the gigglers might revisit - or mummies or ghosts.. you can search for them, too. floor 8 is a bit open spaced, but with a map you should be able to relocate these cleptomaniacs! good luck - also try the side passages and have a warm welcome ready if you meet one.. and a vorpal blade helps with those ghosts
It might also be worth checking the passages below because the giggler could have dropped down a pit and died carrying your shields. Also it could have been hit by a fireball so your shields could be lying around on the floor somewhere.
Blue teleporters remove the fear/retreating-from you-because-I-just-successfully-stole-something-from-you status effect from a monster , and they are all over that level. The gigglers should come back to you with just a little exploring of the level, if they are still alive. That random shield on the ground may be yours and not from a slayed skeleton...