Poor Thumper....! It is so scary when one of the cats doesn't come home when it is darker; I've had this 2 times with Zazou. Both times she came back in the morning.
I hope that Thumper is coming home soon too; maybe he is too overwhelmed now by everything he sees, and by that barking dog. Cannot you ask your neighbour to keep the dog indoors till your Thumper is back?

Please Thumper, hurry home!!