How did you find your lost relative?

Is there anyone here who never knew their mom/dad/both and finally reconnected with them?

My fiancé never met his dad because his mom doesn’t even know who he is or what his name is. She had a one night stand at a party and by the time she found out she was pregnant she couldn’t find him...

I want to help him find his dad, but I’m not sure what is the best way

(23 and me, Ancestry DNA, private investigator, etc any source I haven’t listed that you think is helpful)