Rich tributes continue to pour in for pop legend Whitney Houston, who died on Saturday in Beverly Hills, California.

Celebrities on Twitter were quick to respond to singer's death.

Russell Simmons said he was "deeply saddened by the death of Whitney Houston...may she rest in peace."

"Just heard the news. so crazy," tweeted Justin Bieber, "One of the GREATEST VOICES EVER just passed. RIP Whitney Houston. My prayers go out to her friends and family I am sadden to hear of the passing of Whitney Houston today..."

Mariah Carey expressed her condolences over a series of tweets, saying: "Heartbroken and in tears over the shocking death of my friend, the incomparable Ms. Whitney Houston. My heartfelt condolences to Whitney's family and to all her millions of fans throughout the world. She will never be forgotten as one of the greatest voices to ever grace the earth."

The two main men in Whitney's life - ex-husband Bobbie Brown and her mentor Clive Davis - both expressed their feelings on stage over the weekend's Grammy ceremony.

Bobbie discovered the news while performing with New Edition at a show in Mississippi. At one point in the concert, a teary Brown shouted "I love you, Whitney!" and blew a kiss toward the sky. While performing "Tenderoni," Brown broke down, sobbing and asked the crowd to sing along, US Weekly reported.