Ali Lohan, 17, Looks Rail Thin in Teeny Romper

Ali Lohan doesn't appear to have dined on pineapples or Mahi-Mahi during her Hawaiian vacation.

In Oahu, HI on Monday, the 17-year-old stepped out in a teeny, ill-fitting romper with cutouts at the waist -- a look that definitely did not cover her shockingly gaunt figure.

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Ali, who now goes by her full name "Aliana," hit up the Pacific island to check out the Pipeline Masters surfing competition this past weekend with her sister Lindsay Lohan.

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This is the teen's third scary-skinny appearance this month. On December 6, she turned up to a model casting in Beverly Hills looking pale and frail in skin-tight jeans and a white blouse. Then, just three days later, was spotted in short cut-off shorts and a midriff-baring tank top in Hawaii.

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In a recent interview with Page Six magazine, the model, who's signed to Next Model Agency, said that "she's always had a fast metabolism and is able to eat what she wants, from scrambled eggs with American cheese and hot sauce to Nutella." "I can just eat [it] out of the jar with a glass of milk," she confessed to the mag.

Back in September, Lindsay's little sis denied that she had any plastic surgery done after pics showing her drastic angular face and fuller lips emerged.