She's come under fire for her recent weight loss but Ali Lohan refused to cover up her skinny frame as she stepped out in short shorts and a T-shirt.

RadarOnline.com has the scary new photos of Lindsay Lohan's rapidly disappearing little sister as she ran errands in Malibu Tuesday in her older sibling's Porsche.

Despite the shocking transformation of her young face, Ali Lohan is adamantly denying that she’s had plastic surgery.

Lindsay Lohan’s 17-year-old little sis, who is signed with NEXT Model Management, slammed the idea that she’s gone under the knife, despite pictures that show off her shockingly skinny and seemingly altered frame and face .

“It's stupid,” Aliana (as she wants to be called) said.  “I don't listen to it. It's absolutely not true.”

As the fans worry about Ali Lohan's startling weight loss, Lindsay Lohan is standing up for her little sister.

"I love how haters pick on my sister yet every runway model is just as thin! My sister is gorgeous and I'm so proud of her and her career!!!!" tweeted Lindsay Friday night.

PHOTOS: Ali Lohan Is Looking Scary Skinny

Ali, 17, who just signed a contract with the famous agency NEXT Model Management, was photographed in Beverly Hills on Tuesday and her thin frame caused a firestorm of controversy.

Currently in New York for Fashion's Night Out, 25-year-old Lindsay put her own troubles behind her to defend her younger sibling.  She denied rumors that Ali had work done on her face, after a plastic surgeon offered his opinion that her new look was the result of Botox and fillers.

PHOTOS: Lindsay Lohan And Sister Ali Shop In Venice

As RadarOnline.com previously reported, the girls' father, Michael Lohan, also expressed his concern over his younger daughter earlier this week.

“It’s scary to see my daughter looking like this,” he exclusively told RadarOnline.com. “Ali was always on the thin side but seeing how much weight she’s lost there appears to be a drastic change that concerns me.”

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Dr. Majid Ali, a highly respected nutritional expert, who has not treated the star, estimates that the 5'8 1/2" model's weight could have dropped as low as 95 pounds.

“She is very underweight. By looking at her cheekbones you can tell she has muscle wasting going on," he exclusively told RadarOnline.com "At her height, I'd put her under 100 pounds, maybe 95, and that's way, way too thin.”

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Ali Lohan’s Shockingly Skinny Weight Loss Has Family Worried

Lindsay Lohan's younger sister, Ali, wants to set the record straight about pictures that show her looking skinnier than ever and with what some see as a remarkably different face. Ali has recently signed a modeling contract with Next Model Management.

In an exclusive statement to RadarOnline.com, Ali's powerhouse publicist, Steve Honig says: "Aliana has never had any type of plastic surgery in her life, nor has she ever considered it. Her success as a model lies with her natural looks and she has no interest in changing that.

“During the past two years, she has gone through a normal teenage growth spurt that has made her taller and slimmer. It has also slightly changed the composure of her face, all of which is typical of what happens to kids in their mid to late teens. It’s what most people refer to as the awkward stage. Ali is growing up, that’s all."

A leading nutrition expert estimates that Ali Lohan’s weight has plummeted to 95lbs after seeing the shocking photos of the 17-year-old taken this week.

Lindsay Lohan’s younger sister, who recently signed a modeling contract, looked emaciated with sunken cheeks and skinny arms and legs while out in Beverly Hills, leading to concerns about her health.

“She is very underweight. By looking at her cheekbones you can tell she has muscle wasting going on,” Dr. Majid Ali, who has not treated Ali Lohan, exclusively told RadarOnline.com when he saw the shocking pictures of the teen.

Lindsay Lohan’s little sister Ali, is a brunette beauty with a blossoming modeling career but in these shocking new photos obtained by RadarOnline.com the teenager’s gaunt face is causing alarm in her family.

Ali, 17, was snapped in Beverly Hills on Tuesday and her thin frame is a stark contrast to the healthy looking girl she was just five months ago, when photographed in March.

PHOTOS: Ali Lohan Is Looking Scary Skinny

Watch out Kylie and Kendall Jenner, you’re not the only famous siblings to get a modeling contract!

RadarOnline.com has confirmed that Lindsay Lohan’s younger sister Ali has signed a contract to be a model with the famous agency NEXT Model Management, who have represented stars like Miranda Kerr, Petra Nemcova and Molly Sims.

“In Fashion, Ali will set herself apart as a bonefide icon. One that fashion fans will follow not because of her famous last name, but because of the beautiful images and fashion trends she is helping create,” Alexis Borges, Director, Next LA tells RadarOnline.com.