ICYMI: Tyra Banks is 'Blossom,' Questionable Childhood Style & Shoutouts to Rihanna

Celebrities shared behind-the-scenes images, such as this one by Sarah Michelle Gellar on the set of "Cruel Intentions," and took time to wish Rihanna a Happy Birthday with some old pictures. Check out what else the stars shared for Throwback Thursday:

Kevin Hart: The actor/comedian shared a picture of himself and his best friend in high school. He started the caption by saying, "Ok let the jokes begin..." He said he and his friend were the smallest guys in school, and he can't help wondering why his clothes were so big.

Kevin McHale: Remember the first time Quinn Fabray made a statement on "Glee?" Artie, or Kevin McHale, does. He shared a behind-the-scenes picture of Quinn, Santana and Brittany getting ready to shoot "I Say a Little Prayer."

Kevin McHale: McHale decided to share another Throwback Thursday picture-this time of himself. He wasn't sure what the occasion was, and captioned the image with, "1st communion maybe? Workin that extra big tie."

Lindsey Wixson: Model Lindsey Wixson didn't travel too far back in time. She shared a picture from last season's Fendi show, where she showed off a black bob.

Jason Mraz: This crooner posed with some hilariously placed avocados. He said, "A blossoming avocado farmer." He apparently found this image beneath his fridge.

Usher: Usher shared a picture of a picture of himself as a kid. He has his signature dimples on display and is touching a teddy bear. He doesn't offer any explanation, though.

Common: This rapper is mega cool now, and perhaps he always was? That's what he thinks! "I don't know if it's a collar or a hood or a hoodcollar on my sweater. Anyways, ya boy was fresh!"

Nicole Richie: The designer shared a throwback picture, where she doesn't look very different than today. She does mention House of Harlow, so it might be from when she started her brand.

Tyra Banks: It's hard to believe that Tyra Banks was once just a model, but she was. In this picture, which she captioned with "Flower delivery," she looks like '90s sitcom star Blossom.

Iman: The supermodel shared a picture of Rihanna in honor of her 26th birthday, calling her the most beautiful girl in the world.

Jessica Alba: This Latina actress used to be known as Jessica Marie Alba, when she had skinny eyebrows in the '90s.

Twiggy: The '60s model shared a picture of herself with Michael Jackson in the '70s. "It's so long ago, we were so young," she said.

Cara Delevingne: This It-girl couldn't help posting an old picture of good friend Rihanna for her birthday. "This picture means so much to me because it was the first time we met and you have been such an incredible friend ever since. You are such a strong and truly inspiring woman and i am so lucky to have you in my life! I love you boo and thank you for supporting me through so much"