Dear All, 
   I am trying to find every trace possible, of my family members, who were called Kornitzer and lived in Fiume, Rijeka, Croatia. 
   My grand grandmother was Cecilia Kornitzer - Pollak, her brothers Maks, Milan and Eugen, and sisters Stela, Melanija and Irena. 
   I would be most grateful, if anybody could shed light on the destiny of these people.
   Many thanks in advance.
   Reuven Koffler / Jerusalem 

I suppose you already searched the Arolsen archives. Some of the names are there but they were either from Hungary or Vienna.

Shosh Eizenshtein, Toronto 

Reuven,

A search at The JewishGen Unified Database for surname KORNITZER (using a phonetic search on the surname) and town Rijeka find this:

KORNICER, Armin
born 1862
died 1905
Rijeka / Croatia

The same search for POLLAK and town Rijeka finds several people with that surname buried in Rijeka.
One mention of POLLAK in Hungarian marriages, and one in Hungarian deaths.

And, several people named POLAK / POLLAK at Yad Vashem in connection to town Rijeka and Fiume.