McCallum was last seen leaving her grandmother's home in Montvale, New Jersey on March 11, 2015. She was driving a black 1998 Subaru Impreza with the New Jersey license plate number N32-EAY. She has never been heard from again. Her vehicle was later found abandoned in Long Branch, New Jersey.

There were no indications that McCallum had planned to run away. She was staying with her grandmother when she disappeared, but had stopped at her parents' home the night before to pick up a phone charger. She left all her clothing and belongings behind, as well as her dog, whom she adored