There's services that do this automatically for a price, and they've been around for a while, for e-mail, phone numbers, and much more. Any bits (literally, bits) of information given without authorization (or plausible belief it's the intended user on the other side) will be efficiently put together from a variety of sources, as there's no shortage of incentive, and many all over the world prodding services used by billions of people worldwide. And then eventually leaked..
There used to be deep web services that provided a lot of this stuff for free back in the early 2000s or so. I think everything like that is behind at least some level of paywall now but it's not hard to get a fairly complete dossier on someone given a bit of background information and a pretty small expenditure.
