talk to them in discord and predend to be a vulnerable kid, get pretend-groomed, reveal made up personal information (but keep the story straight, no contradictions), they might reveal information in responce. try not to ask them anything directly, people are more likely to talk when there's awkward silence. basically groom them into trusting you when they think they are the ones doing the grooming lol
try to find out how many sibilings they have, other family members, possibly their names. even if your target isn't the type of person to share every second of their life online, their clueless normie loved ones often are and their facebook and instagram pages can be a goldmine of information (been there done that can confirm). try to get some clues about state they live in, pictures of view from their window, where do they study or work.
there's probably an easier and quicker way to doxx someone if you are tech-savvy but I'm not like that, so this is what I would do