The following is a work of fiction:
Myself and some colleagues have recently been working out reliable, reproducible, and empirically proven methods of inducing moral panics and mass hysteria events in vulnerable populations entirely memetically and without spending a single penny or lifting much more than a finger.
The first problem is what exactly makes a population vulnerable to moral panic/mass hysteria. These conditions would seem somewhat analogous to fuel-load and climatic conditions that increase the likelihood of wildfire in ecological systems. But in human populations these are of course psychological/social/economic/etc. conditions rather than purely physical. High levels of anxiety and uncertainty in a population, or in contrast - far too much certainty causing such a gross mismatch between expectations and outcomes that severe levels of cognitive dissonance result; interpersonal, familial, communal, and government level repression, rapidly shifting demographics, social/cultural/informational isolation, poverty, low levels of education and intelligence, high levels of conformity and "social contagion factor", youth, immaturity, gullibility.
Assuming there is critical mass of fuel-load and ripe socio-climatic conditions in a population the second problem then is a memetic triggering event. This could be a real physical fear-inducing event or a perceived one. But our concerns here are only with the theoretical and memetic: A newspaper report, a rumour even, a sighting of mysterious and unexplained phenomena. If the ideological substrate of a given population has become unstable and volatile and delusional enough it could be something as simple as a person experiencing a nightmare from which they awaken believing they have suffered some kind of supernaturally caused but real-life harm. Somebody who thinks they've seen a ghost or heard a witch utter a magic spell under their breath. A tree falling down in the middle of the night in the forest for no particular discernible reason may produce in a paranoid and guileless person a sense of immense and inconsolable dread. Someone or something, presumably, is to be blamed. And from blame then on to hunt and retribution. And from then on to who knows where.