My Idea

This idea may vary to my final trailer, but this is my initial idea:

Outline of the story:
A teenage girl's parents have gone away for the weekend, and, so she isn't left home alone she invites her two friends over to stay with her, because although the house isn't 'stereotypically' creepy, when the girl is the last one awake at night she feels that the house develops an eerie atmosphere and she feels as though she is being watched by somebody. As she explains this to the friends one of them laughs off the comments and tells her that if she means her house is haunted, it cant be as ghosts don't exist.
The evening the friends arrive all is well to start off with, until night falls and as they are settle down to watch a film, one of the friends decides to go and get a box of chocolates she had brought with her for them all share. The friend is gone for quite a long time and the other two girls get suspicious as to why it has taken her so long - little do they know that whilst the friend was upstairs getting the food from her bag, a young girl had 'appeared' to the friend. It would not be seen as to what happened to the friend, only that when one of them goes to find her she has seemingly vanished into thin air, with only a note left saying 'who says ghosts don't exist' written in a child's hand writing. From then on, the young girl would 'appear' to the two girls, haunting and terrorising them throughout the rest of the night, with her aim appearing to be to kill them.

Trailer outline:

• The teenage girl invites her friends over on Saturday, explains about parents being away and why she doesn't want to be alone
• One of the friends then makes the key 'ghosts don't exist' comment 
• Cuts to the two girls arriving at the house
• The three girls settling down to watch the film - one of the guests makes her excuse to leave the room and heads upstairs
• The friend looking through her bag - can't find the chocolate
• Suddenly the bar/box lands on the middle of the floor
• Friend slowly looks up to above the doorway (there should be a window there but it had broken and so is just an empty space) where there is a young girl staring at her
• Friend panics and picks the chocolate up off the floor to throw at the girl - as she bends down she looks up to see the girl now in the room standing in front of her
• The two remaining girls get suspicious of the others absence, one goes upstairs to find her, the other goes to the toilet
• The one that goes upstairs walks into the empty room and as she turns to leave she notices a note on the wall that has been written by a child saying 'who says ghosts don't exist?'
• Meanwhile, The other girl in the bathroom is looking in the mirror when suddenly a child's hand slaps against the window 
• A montage of clips showing the girl appearing to them would then be shown (included in this montage would be clips showing that all the doors and windows are locked as well as all keys hidden - there is no escape)
• The screen then suddenly go black
• Fading in would be a shot of a young girls hand pulling a knife from the block - the screen would then suddenly go black 
• Fade in again for title of the film and the release date