<human>: Bit of the back story:

A few years ago, my dad drunkenly revealed to me that when he was younger, he ended up having a relationship with a German girl he met on a school trip when he was 16.  After a few repeat visits, it then turns out that he gets her pregnant, and attempts to somehow look after her and the baby, traveling back and forth between the UK and Germany.  Months down the line, she sends him a letter, telling him that she has met someone else, and they are going to try raising the baby together, and that he should move on.  Initially, I was pissed off beyond compare, and sometimes still am, but then I repeatedly think about the fact I possibly have an older brother or sister somewhere,walking about in Europe, oblivious to my existence.

To this day, his own mother, nor my own whom he is still married to, knows about it.  Only my grandfather and I were ever told.  How no-one else ever found out astounds me.

Since then I have been wondering if I should try and find my half brother or sister, with my infantile grasp of the German language and internet know-how.  

Only recently, out of the blue, he has asked me to try and track down the woman, so he can apologise, for what he sees as essentially ruining her life, getting her pregnant at such a young age.  I only know one person in Germany who is willing to help but I have a hard time communicating with them on a regular basis.

All I have to go by is a physical description of her when she was younger, a name, and a town.  That's it.

How can I manage to accomplish this?  Anyone out there have advice or similar "sibling hunter" scenarios?

Can you provide a brief overview of the text?
<bot>: dad got a girl in Germany pregnant when he was a teenager, now asking me to find her for him, have no idea where to start.