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Auditions were usually the same for Amber Riley: She would belt out Chaka Khan's "Sweet Thing," producers and casting agents showered her with praise, and then-silence. "The feedback was, 'You're a great singer! You're a great actress!' And then I don't get the call," says Riley. Instead, the size 16 actress often heard, "I was a little big for the role or 'She's not the look we want,'" recalls Riley. "It hurts for a minute. But being told no just made me work harder."

It took 14 years for Riley to finally get her big yes. After juggling a day job at Ikea and singing backup at clubs along L.A.'s Sunset Strip, Riley, 24, landed the role of Mercedes Jones, the "brassy, full-figured, confident diva" with powerhouse pipes on the hit musical comedy Glee. While she's delivered memorable renditions of "And I Am Telling You I'm Not Going" and "Bust Your Windows" on the series, the singer-actress struck a chord with Gleeks during a recent episode in which her character bucks orders to drastically drop 10 lbs. and ultimately learns to be comfortable in her skin. "I had to go to a place that was very vulnerable," she says. But the payoff is worth it: "When I receive letters from girls that say, 'You give me confidence,' I think, 'Wow, this is amazing.' That's my goal: to let people know it's truly what's on the inside that counts."

It's a message the 5'2" star learned as her weight fluctuated growing up in La Mirada, Calif. A self-described "beanpole" as a child, "I was actually made fun of for being a skinny kid," says Riley. But like her older sisters Toiya, 34, and Ashley, 26, Riley slowly packed on the pounds during high school. The culprit? "Hormones and food," says Riley. "I was a size 8. I didn't think that was fat."

But for a teen with dreams of becoming the next big star, "I could tell it would be hard for me to break into the business because of what the Hollywood standard is," says Riley, who stopped going out for roles briefly in high school because "rejection at a young age is hard. You internalize everything and think, 'Is there something wrong with me?'" Singing gave her solace. "My voice and my gift gave me confidence," she says. And even when she was turned away from American Idol during an early round of auditions in 2005, "I was crushed," she admits, "but I didn't let it be a setback. I made it my motivation to do better."

By 2008 Riley was ready to step back into the acting arena when she heard about a comedy series looking for vocal talents. Nervously, she went through her usual motions for an audition. Only this time, instead of silence, as soon as she finished wowing Glee creator Ryan Murphy, "he was taking me around to people saying, 'Sing for them!'"

These days, to keep her energy up for her 17-hour days on-set, Riley-who last stepped on a scale two months ago and weighed 190 lbs.-runs for up to an hour three times a week. As for her diet, "I don't deprive myself," she says. "But I want to be healthy." And while she sometimes experiences twinges of self-doubt ("I dislike my gut, but who wouldn't want ripped abs?"), overall Riley embraces her body from top to bottom. "I love my breasts, my face, my butt," she says. Most importantly, "I love myself."