Looking for Pieko Family of Germany

My fathers' name was Herbert Wilhelm Pieko. He was born january 23,1916 in Konigsberg (ostpreuben). My mother Margarte mast was born July 23,1907 in Bartenhof also Ostpreuben. My name is Irene Pieko Hallgren. We migrated to the u.s. in 1951. I have been searching for living relatives and have always ended up in a dead end.
My mothers mothers maiden name was schlemminger and she married Arnold Mast. I think the had at least 8 children-one of course my mother and I remember her mentioning a two brothers one arnold in switzerland and anther fritz-they have both passed away. Also a sister Emmie and also Elisabeth. I don't recall any other. My father had a half brother Gustav Meyer which was residing in Berlin. I recently sent a letter to him and it was returned. I have reason to believe that he also has passed. I would like to find out if I have cousins or any other immediate family. I have a brother named Bernhard that resides in Chapman,Nebraska. We are the only two here that I know of. My parents are both deceased. I would appreciate if you find anything that would be helpful. Thanks.

Yours truly,
Irene Hallgren