I found my bio father by joining a service online, it cost me $39.00 for three months, the fourth phone call I made found my 1/2 brother, my father had already passed, I had been looking for him since 1974, I don't know if it was a fluke or just that technology had become that good over the years. I never would have had or had had the $$$ to hire anyone, that is why it took me so long.
You need an approx. DOB, last known or best that you can find place of address, if you know of any other children you think he/she may have had, THEIR parents info if you can find it, etc..The more you can input the better the outcome.
Good Luck!
The site I used has changed the name I will go online later & see if I can find what it is later & can send you a message.