Ashlee Simpson-Wentz‘s weight is plummeting – and her friends say it’s because she’s almost obsessed about her role on Melrose Place.

The 25-year-old actress has been crash-dieting and stressing over how she measures up to her gorgeous co-stars on the CW series, say pals.

“She doesn’t seem to eat much anymore and went from a size 8 when she was pregnant to not even filling out a size 0 now. She’s barely above 100 pounds,” one friend revealed to The ENQUIRER.  The actress stands 5-foot 6 inches.

“She substitutes Red Bull for some meals, and snacks on nuts and other small things instead of having a decent lunch or dinner.”

Ashlee, who gave birth to son Bronx Mowgli November 2008, plays Violet Foster, a small-town girl who is trying to make it big in Los Angeles.

Since Ashlee accepted the Melrose job, friends say she’s placed tremendous pressure on herself to lose her extra pregnancy weight.

In addition to the crash diet, she used a program developed by celeb trainer Ramona Braganza called “321 Baby Bulge Be Gone,” which incorporates cardio and strength training sessions.

“It was almost as if she was obsessed with looking as good as possible for all the show posters and advertisements,” said the friend.