Demi Lovato lashes out at superfan Stalker Sarah for allegedly taking advantage of her younger siste

"Stay the f**k away from me and my family."

Demi Lovato has lashed out at Stalker Sarah after accusing the superfan of taking advantage of her younger sister Madison.

In a post on Stalker Sarah's Instagram page - which has since been deleted - the 'Stone Cold' singer reportedly wrote (via Sugarscape): "THIS IS MY 14 YEAR OLD BABY SISTER. You are a 20 year old fame LEECH. SHE IS NOT YOUR BABE...

"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.

"My family is not afraid to press charges... I'm not your f**king '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**k away from me and most importantly my family."

Demi and Sarah have been photographed together in snaps previously shared on Sarah's social media account.

Sarah's Instagram page is full of pictures of herself with celebrities, including Rita Ora, Justin Bieber and Niall Horan. She describes herself as a video blogger and promoter in her Twitter bio.

Madison De La Garza - who is best known for playing Gabrielle Solis's daughter Juanita in Desperate Housewives - is Demi's maternal half-sister. Demi has an older sister, 28-year-old Dallas, who is also an actress.

Demi was recently awarded the Vanguard prize at the GLAAD awards in LAfor her contribution to the LGBT community.