The 20-year-old woman who calls herself Stalker Sarah outraged Lovato by befriending the star's 14-year-old sister, Madison de la Garza.
Lovato blew up when she saw one photo of her little sister and Stalker Sarah with the caption: "Crave with my love."
Lovato, 23, took to Instagram to blast Stalker Sarah for getting too cozy with her little sister.
“THIS IS MY 14 YEAR OLD BABY SISTER. You are a 20 year old fame LEECH. SHE IS NOT YOUR BABE," Lovato wrote on Instagram Friday.
“For anyone reading this: this girl has no regard for anyone’s well being but her own. She completely takes advantage of people, even 14 year olds even though she’s 20.”
She added: “My family is not afraid to press charges,” before deleting her posts.
Under an older photo of her and Stalker Sarah together, Lovato wrote: "I'm not your f___ing 'girl.' If I was you [I] would not be asking for pictures. You STALK PEOPLE FOR A LIVING. We are NOT FRIENDS. Stay the f___ away from me and most importantly [my] family."
She deleted that comment as well.