Find people in Cologne

Hey there , hope you guys all doing well ,
This is my first post hope I'm not posting in wrong section,
It's regarding to find someone in Cologne , whom my father met in 1980,  I have his old business card and his address,tried a lot of online telephone directory but couldn't find them ,is there any other way to find?
I have his old telephone number, but obviously it might has change.....

By the way I'm not in cologne right now , I was there last year , I tried to find that time , but because of time I couldn't, might I'll be visiting Germany again next month, if there is any other way , Please do let me know.

Much appreciated
Thanks :)

Of course information from a 36-years-old business card is not the best starting point - after all the person might be dead or gave an incorrect name. But if you have his (registered) residential address, you can engage a lawyer to trace his moves until the current address is found. This works because it is mandatory (by law) in Germany to always register your residential address with the authorities. (It might not work if he moved abroad.)
If he was the business owner, you can also try to consult business registries to see if it or a successor company still exists.

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