I know to some extent of what your going through, I am searching for my sister who was given up for adoption in 1968 by my mum, through no choice of her own. Mum wasn't allowed to keep her baby and was made to give her up for adoption by her parents. There isn't a day goes by when mum doesn't think about her. Have you tried posting messages on adoption sites, there are many sites where you can post/search messages for free, i have posted messages on many of these sites and some people will email you offering advice.
hope this helps and good luck with your search
best wishes x