There's No Place Like Here by Cecelia Ahern

Sandy has been fascinated with missing items after her childhood classmate vanished twenty years earlier. To find what was missed is her one purpose-from the one sock which falls in the laundry machine to her missing car keys. No wonder, though, that the job of Sandy 's life would locate people who have separated from their loved ones. The family of Sandy is perplexed and troubled about her rising worry. Her parents can't grasp her compulsion, and she's driving them away by losing herself to track these missing people. She gives up her life to give the shattered families a drop of hope and to avoid the deceptions of her