Ok, real talk. You don't need to go tell a person all the mean things being said about them. Especially if that person has already been on the receiving end of direct harassment. Likely, that person already knows and if they don't you're adding on to the harassment 1/
They are already getting. So I know that you mean well, but doing that actually more likely is doing harm than helping. Don't magnify the harassment, even if you mean well. If they ask for people to do so and report to them, ok, fine. But don't do it unasked. 2/
Of course, of it's threats against them and their home address is listed. Then that may require police reports. (and I mean credible, violent threats, not generic "I hate them and wish they'd die" kind of thing.) 3/
Just think before doing something. Not everything needs that persons attention. If you are worried, of course monitor it! That's the best thing to do. If you're upset about it, think how the target will feel. Is them knowing important enough to make the harm of knowing worthwhile