Today on Twitter, Ryan Seacrest tweeted his thanks to Selena Gomez and Joe Jonas for making appearances at the launch of his media center called he Voice in the Children's Hospital of Philadelphia. According to the American Idol host's website, this media center, which will include a studio, will give sick children a creative outlet. Seacrest opened a similar center in the Children's Healthcare of Atlanta. Meanwhile, Mariah Carey tweeted about her new set of twins and Mark Hoppus tells us who really invented planking. See what your favorite stars were chirping about today!