I had this problems with a grt grandfather. I used a mix of DNA info and traditional genealogical methods. As Annie says, don't rely on the matches' trees but use them as a guide.
If you've identified a shared group, what range of cMs do they share with you? Also, is there anyone there who has a tree that you can verify? Have you messaged any of them to find out more about their lines? If you're lucky, you will be able to identify a common ancestor from the group. Then investigate locations, etc.
It took me about 3 months to identify the correct 'father'. I checked my info at each step and didn't use the Leeds method but used my own tried and trusted routines!
Gadget