Her necklines have plunged, she's plying the all-night party circuit with new best pal Paris Hilton, and she has even ditched her panties.

As if to prove, as she once sang, that she really is "not that innocent," newly separated pop star and mother of two Britney Spears is letting it all hang out--shocking her fans, causing concern among friends and making herself the butt of jokes on late-night TV.

"Girls Gone Wild!" Us Weekly magazine blared in its cover story this week, charting a manic two weeks in which Spears was seen gambling all night in Las Vegas, spent time nightclubbing and shopping with "celebutante" Hilton, and was photographed on several occasions climbing in and out of cars without panties.

The latest media frenzy over Spears comes two years after she put her recording career on hold for motherhood and three weeks after filing for divorce from husband Kevin Federline.

"Lately, I hear things and see things, and I'm just wondering, 'girl, WHAT IS UP?' Please stop acting like someone you're not. WEAR UNDERWEAR!!" pleaded one longtime fan on Spears' Web site Thursday.

Talk-show host Rosie O'Donnell, who has jokingly offered to adopt Spears and her two baby sons, Thursday offered her a gift--a pair of red panties inscribed "No Peeking."

But celebrity watchers say the singer, who shot to fame with her debut 1998 single, "... Baby One More Time," and the accompanying video in which she dressed provocatively in a Catholic schoolgirl's uniform, appears to be enjoying the limelight.

"Britney is succeeding in getting us to talk about her. From the beginning, Britney has made her career out of shocking us, and she ultimately will win because of it," Ken Baker, West Coast editor for Us Weekly, told Reuters.

With Federline--now dubbed Fed-Ex by the tabloid media--out of the picture, Spears has been inseparable from Hilton for the past two weeks.

On one occasion, Spears and the hotel heiress split a pair of fishnet stockings and each wore a leg. On another, they were pictured in coordinated leopard-skin outfits--Spears wearing a thigh-hugging, cleavage-baring mini-dress.

Spears, who turns 25 Saturday, was seen this week shopping for thongs and corsets at a Hollywood lingerie boutique. Celebrity Web site TMZ.com said she spent more than $3,000 at the store. But the following day, she was photographed again--in another open-leg crotch shot.