"Reveurs" are members of the unoffical fan club for The Night Circus.
The creation of the Reveurs began with Herr Friedrick Thiessen, a clockmaker, who became devoted to the circus. Herr Thiessen wrote multiple articles and reviews praising the circus and exploring the many components which make up the remarkable spectacle. Over time, people who read the articles wrote back to Herr Thiessen, sharing his enthusiasm for the circus. This lead to Herr Thiessen becoming the unintentional leader of the Reveurs.
The name "Reveur" is in reference to that alternate title for the circus - Le Cirque Des Reves. "Rêveur" literally means "Dreamer".
Reveurs can be recognised within the circus through their unoffical "uniform" - a reveur will normally wear black and/or white clothing, with a red accent (such as a red scarf for example). This stems from a comment made by Herr Thiessen - he wears black and white clothes to blend in with the circus, but the splash of red is a reminder of his position as a follower.