The famed author added a simple note of condolence to Rickman's wife Rima.
"My thoughts are with Rima and the rest of Alan's family," she wrote. "We have all lost a great talent. They have lost part of their hearts."
Daniel Radcliffe, who acted opposite Rickman in all eight Harry Potter films, also paid tribute.
"Alan Rickman is undoubtedly one of the greatest actors I will ever work with," Radcliffe wrote on Google+. "He is also, one of the loyalest and most supportive people I’ve ever met in the film industry. He was so encouraging of me both on set and in the years post-Potter. I’m pretty sure he came and saw everything I ever did on stage both in London and New York. He didn’t have to do that. I know other people who’ve been friends with him for much much longer than I have and they all say 'if you call Alan, it doesn’t matter where in the world he is or how busy he is with what he’s doing, he’ll get back to you within a day.'
"People create perceptions of actors based on the parts they played so it might surprise some people to learn that contrary to some of the sterner (or downright scary) characters he played, Alan was extremely kind, generous, self-deprecating, and funny. And certain things obviously became even funnier when delivered in his unmistakable double-bass.
"As an actor he was one of the first of the adults on Potter to treat me like a peer rather than a child. Working with him at such a formative age was incredibly important and I will carry the lessons he taught me for the rest of my life and career. Film sets and theater stages are all far poorer for the loss of this great actor and man."
Emma Watson shared this note on Facebook.
"I'm very sad to hear about Alan today," she wrote. "I feel so lucky to have worked and spent time with such a special man and actor. I'll really miss our conversations. RIP Alan. We love you."
Emma Thompson, who frequently worked with Rickman, penned this tribute.
"Alan was my friend and so this is hard to write because I have just kissed him goodbye," she shared in a statement.
"What I remember most in this moment of painful leave-taking is his humor, intelligence, wisdom, and kindness. His capacity to fell you with a look or lift you with a word. The intransigence which made him the great artist he was — his ineffable and cynical wit, the clarity with which he saw most things, including me, and the fact that he never spared me the view. I learned a lot from him.
"He was the finest of actors and directors. I couldn’t wait to see what he was going to do with his face next. I consider myself hugely privileged to have worked with him so many times and to have been directed by him.
"He was the ultimate ally. In life, art, and politics. I trusted him absolutely. He was, above all things, a rare and unique human being and we shall not see his like again."
Rupert Grint also released a statement to Just Jared.
“I am devastated to hear about the passing of Alan Rickman," the Ron Weasley star said. "I feel so privileged to have had the opportunity to work with him on numerous occasions. Even though he has gone, I will always hear his voice. My thoughts are with his friends and family at this time.”
"We are all so devastated to lose Alan," Kate Winslet said, according to The Hollywood Reporter. "He was loved enormously by so many. He was an exceptionally warm and giving man and an utterly phenomenal actor and gifted director. I remember being so intimidated by him when we worked together when I was 19, because he had such a powerful and commanding presence. And that voice! Oh, that voice... But the reality of course, was that he was the kindest and best of men. Had the patience of a saint. He was a warm-hearted puppy dog, who would do anything for anyone if it made them happy. He was a loving and devoted partner to Rima, and like so many of us in our vast industry, my life was enriched by knowing him. My heart goes out to his family and those he loved."
"Alan was a towering person, physically, mentally, and as an artist," Helen Mirren shared, according to THR. "He was utterly distinctive, with a voice that could suggest honey or a hidden stiletto blade, and the profile of a Roman emperor. He was also a great friend, generous and social. He will be very missed by many."
I was at Leavesden Studios today when I heard the news. As I walked through the canteen I thought of Alan queuing up for his lunch with us mere mortals. I recalled the trailer in which he offered me some of the greatest advice I ever received about this mad profession we shared. Being back in those corridors made me remember a lot of things and I will treasure those memories all my life. He inspired my career more than he ever knew and I'll miss him.