I created a social network in 2000. You could friend people, send messages, posts, follow and so on. Unfortunately I didn't have money to expand the capacity and when I added crowdfunding feature, some people were threatening me with reporting it everywhere and sending me nasty messages. Unfortunately I didn't have strength to go through this and I closed it. At peak I had over 50000 active users, but I didn't know how to deal with all threats.
I remember a few - for example someone would introduce themselves as a lawyer and then point out that some clauses in t&c are illegal and that he will report it "to authorities" (and sometimes they would offer "help" if I pay), or someone would upload their nude pictures and then report this to hosting provider that the website is showing these pictures without their consent. Some people would demand that I give them access to private messages of their "partners" and would threaten me that they will find me and "sort me out". Sometimes I had technical issues where the server would go down for a couple of hours - so there was a profile of a local band, something like a Facebook pages are now, and they made a post about the concert they are going to have, but the server was down on that day and they blamed me they lost money because just a few people came to the concert. I also had someone claiming to be a partner of one of the users demanding that I delete his partner account as she ignores him and only spends time on the website and sent me my home address. Very stressful.
edit: I remember one more. One guy would post his nude pictures typically exposing his face and his bottom and then he would write his name and address and add messages like "beat this guy up", "come find me" he would register other accounts and then post degrading comments under these pictures of himself. I initially thought that this is some kind of revenge and I was promptly deleting this and removing these accounts. Eventually that person would write that this is turning them on and was very upset that it gets deleted. It's when I added IP blocking and blocked all addresses he used.
That userbase level is about when you start getting early - usually non-serious - threats and your privacy as a founder starts to erode. Anybody that builds something successful on the Internet will have to disregard the early threats and push forward (or fold up the tent and go home).
When you have 50k or 100k users and you start removing a few dozen abusive users per day, the odds are some of them will be actual lunatics, and some percentage of those will flip their lids and start targeting you with abuse in a surprisingly obsessive way (because they're actually mentally ill). If you can hide behind a faceless corporation with lots of venture capital, that makes it a lot easier as a founder, as the corporate nameplate and lawyers can perform shield duty. If you're a solo founder or equivalent, you take the full exposed hit.
