the Austrian phone directory www.herold.at
has no Friedbergers around Waidhofen/Ybbs, but a few inside the province of Lower Austria (select English as your language and that province under 'Region').
A search with 'no restriction' shows some 41 people, maybe too many for writing letters to all of them. OTOH you could start with the Lower Austrian bunch, and proceed with other provinces later on.
If there were any people from your original family left who just moved to other places, chances for them to have moved towards Upper Austria or into Styria would've been about the same... My bet though is mainly with Lower Austria (Bisamberg/Langenzersdorf is quite close to the capital of Vienna) and of course Vienna itself (4 people).