Your best bet is the phone book.
Find online phone directories for Prague (because it's a large city and the books should be easy to find and the city draws people from many places around the country). Of course, if you know the towns your family is from, aim for those books.
Look for city directories (from times before phones existed or were common).
Ancestry, FamilySearch, etc.
Anything else you can find.
If your family is Jewish, use JewishGen to search for surnames and see where yours turns up (don't worry about variant spelling).
These techniques will also tell you which countries your surname might be found in. For example, it may turn out a large number are in Slovakia, or Austria.