I think by going through a person's posts and seeing what they've said about themselves and taking every bit of disclosed information and using it to try to build a picture then looking for people who tick all those boxes.
Hugely problematic. First of all the person may well have lied about things. Secondly, the chances of misidentifying someone are high. Even if all the things they said about themselves over the years was true, the chances they are unique is low.
You cant just say oh, X poster said they live in London, work in finance and have blonde hair and look at this fb profile. This woman lives in London, works in finance and has blonde hair therefore this is her haha gotcha you thought you were anonymous...
And the person doing this 'unmasking' is themselves anonymous so how can they be held accountable for misidentfying someone and for the consequences of that?