When Abby is barefoot in the snow, Chloë Grace Moretz was really barefoot. During filming the crew had to heat up her feet in between takes so she didn't get too cold.
The Morse code message shown at the end of the official trailer spells out the words "Help Me".
Director Matt Reeves modeled the physical appearance and personality of Abby (Chloë Grace Moretz) after seeing photos of a 12-year old homeless girl taken by Mary Ellen Mark. Moretz said the sadness of her character was decided on by her and Reeves after seeing the photos.
(at around 1h 21 mins) The word "vampire" is only said once in the film.
Colin Moretz: (at around 44 mins) The arcade counter attendant is played by the brother of lead actress Chloë Grace Moretz.