A pile-on ends when people lose interest. A campaign is organised to outlast your patience.
The thing that makes it different
Individually, the messages in a campaign are often unremarkable — mild enough that each one, shown alone to a moderator, looks like an overreaction to report. The harm is entirely in the accumulation: fifty unremarkable messages a day, from fifty accounts, indefinitely.
That is also why the law, where it engages at all, tends to think in patterns rather than incidents. In England and Wales, [1] And where a campaign targets more than one person — a team, a family, colleagues — [2]
The practical lesson from that is about evidence, not about law: a single screenshot rarely represents what is happening to you. A log does.
Why disengaging does not end it
The rest of this site will tell you, correctly, that most provocation depends on your participation. A campaign is the case where that stops being true, for three reasons:
You are not the audience. Much of it is performed for the people organising it, and your reply was never the point.
It is distributed. No individual participant needs to care very much, or for very long, for the total to be relentless.
It has momentum. Campaigns routinely continue for weeks after the target has stopped posting entirely — which is the plainest possible evidence that silence is not the mechanism that stops them.
Not replying is still right. It is simply not sufficient, and the gap between those two things is where people are left without help.
What actually helps
Keep one log, not a folder of screenshots. Date, time, account, what was said, where. It is dull and it is the single most useful thing you can do, because it converts an experience nobody else can see into something a platform, an employer or a police officer can act on.
Let someone else read the messages. Delegating the log to a trusted person is a recognised approach and it removes the worst part — re-reading it all yourself.
Report the pattern, not the message. Platform forms invite you to report one item. Where there is any free-text field, describe the campaign and say how many accounts and how long. A single mild message reported alone will be declined, and that declined report then becomes evidence that nothing is wrong.
Involve the institutions that are already implicated. If your employer, university or professional body is being contacted about you, they are part of this and are better told early than surprised late.
Use the moderation tools that reduce volume without deleting your record — muting, restricting replies, filtering. Volume control is not the same as disengaging, and it does not destroy evidence.
Get an advocate. The services on the support page do this routinely, and can keep going when you have not been able to get anywhere on your own.