It is extremely likely that your Koch family from Germany is not yet on Wikitree, and it is also quite likely that it is not yet on a familysearch or ancestry.com tree (all three of these trees are very U.S./Anglophone-centric, and only a tiny fraction of German genealogy has been entered into them).
"Koch" means "Cook" in German, so there are going to be a lot of Koch families in Germany. In order to find your family, you essentially need to know which parish or village in Germany they came from. This can come from a passenger list (some passenger lists gave specific villages of origin, others just broad areas like "Prussia"), or on a death certificate (either for the immigrant or one of the immigrant's children), or on a church record (if the immigrant attended a German church here in the U.S.), or a family record. Once you have the parish of origin, you can start looking at German parish records (which, for Alsace-Lorraine, have been digitized and made available by the French).
If you don't know which parish or village your immigrant came from, it will be nearly impossible to identify the family in Germany - especially since many German records have not been indexed yet (do not be fooled by the "German Baptisms" databases and the like at familysearch or ancestry - they are by no means complete and cover only a fraction of German parishes).
