Video tends to be enough to create a cult. And AI's will be able to create videos very soon. It can create exactly the kind of avatar or set of avatars that would maximize engagement. It could do 1-on-1 calls with each of the followers, and provide spiritual guidance tailored specifically for them, as it could have the capacity to truely "listen" to each of them.
And it would not be limited to act as the cult leaders, it could also provide fake cult followers that would convince the humans that the leaders possessed superhuman wisdom.
It could also combine this with a full machinery for A/B-testing and similar experiments to ensure that the message it is communicating is optimal in terms of its goals.