Film PR agencies help popularize upcoming movies through press releases / news releases and mentions on online media channels. They start PR activities right after the film is announced and keep offering sneak peeks into the shooting scenes, gossip from film sets, and quotes from the film cast.
They communicate with film journalists and give out positive communications and reactive stories when required.
These agencies ensure that the viewers stay updated about the progress of the film after it is announced. This way they keep them interested and intrigued and are critical for the success of a film.