Hi @Simi
You can request information about another person at your local citizen's registration office (Meldeamt/Bürgeramt/Meldebehörde). You request what is called 'einfache Melderegisterauskunft' about the person. You need to provide the following information if you have it: first name, last name, gender, date of birth, last known address.
If they have a record of the person, they will provide you with the following information: first name, last name, current address and if the person is deceased.
Here you can read about the process in different parts of Germany:
https://verwaltung.bund.de/leistungsverzeichnis/DE/leistung/99115004001001/herausgeber/BW-84/region/08111
Best,
Éanna