Online Yellow Pages?

Well, since you didn’t specify the country I’ll assume you live in Denmark, and www.dgs.dk or www.krak.dk are the best ;-)

I wouldn’t know about the age groups, but they probably correlate to the ages most likely to use the internet.

I haven’t found any online yellow pages to be useful. There are not enough participants, and therefore, they are too incomplete to be of any use.

I use anywho.com. I don’t know how many users they have though.

I was going to say the same as @YARNLADY

I find everyone I’m looking for at anywho.com. Some just don’t have a big add. My apartments don’t pay to be there, but they’re listed anyway, just not in bold and not with a big ad