Yup, provide a time-limited contest : "December 1st (or whaterver), come back to see the winner!". This could create quite a viral loop. Also, try to provide

Yup, provide a time-limited contest : "December 1st (or whaterver), come back to see the winner!". This could create quite a viral loop. Also, try to provide a sense of tribe : make people sense they belong as fans of a certain movies. This will greatly increase their participation.