"RIP a legend," Libeskind wrote on Instagram.
"At dinner with him in Berlin years ago, we shared our mutual passion for drawing. You can see in his brilliant buildings a mastery of architecture's millennial tradition. He will be missed."
Foster has written a 300-word tribute to the man he said has created "a powerful body of work that has shaped contemporary practice in a major way".
"For me, he was an inspiration and a true master of monumental modernism," Foster said.
"He is one of the greats and will surely be missed by us all. Yet, he leaves behind a formidable legacy that will continue to influence architects and designers for decades to come."
"An incredible man, an incredible life"
Chinese architects in particular held Pei in high esteem, as a homegrown architect who gained international acclaim.
Architecture and design curator Aric Chen also paid tribute, sharing an archive picture on Instagram, showing IM Pei in his signature round glasses and three-piece suit leaning against a geometric patterned wall.
"An incredible man, an incredible life," wrote Chen, another Dezeen Awards 2019 judge.
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"The passing of IM Pei saddens me as much as it gives me hope," wrote Huang.
"From his Chinese roots, being a minority at Harvard University to later creating the world's finest architecture including The Louvre, The Bank of China Hong Kong, the John Hancock Building and Museum of Islamic Art, which all form part of my education and memories," she added.
"His piece of advice? He wished he designed far fewer buildings."
"The end of an architectural era"
Architecture critics joined the praise of the venerable Pritzker Prize-winning architect, whose buildings include the pyramid at the Musée du Louvre in Paris and Hong Kong's Bank of China Tower.
Architecture critic Paul Goldberger said it was "the end of an architectural era, truly" in a series of posts on Twitter.
"It makes me feel a sense of nostalgia for the idea of a building as something to believe in," he said.
Financial Times critic Edwin Heathcote said Pei was "a very nice man".
"No histrionics, always dapper, gentle, modest and considerate and no arrogance at all," he wrote on Twitter.
"The last surviving modernist"
RIP IM Pei, the last surviving modernist, who has died at 102. Memories of this museum in his hometown of Suzhou next to the 16th-century Garden of the Humble Administrator, a UNESCO site from which he drew such inspiration. pic.twitter.com/aFOcUqCB6Q
— Christopher Turner (@TurnerOnDesign) May 17, 2019
"The most identifiable landmarks of Hong Kong – the Bank of China Tower designed by IM Pei and Partners, finished in 1990. It was the tallest building in Asia until 1992, the first supertall skyscraper outside the United States to break the 305 metre mark, and the first composite space frame high-rise building," wrote Choi.
"Thank you and RIP"
"His loss is immeasurable"
Other figures that joined in the public mourning for Pei include American actress Emmy Rossum.
"To come into the world and fill it with art and leave it a better place than it was before," tweeted Rossum. "RIP IM PEI."
"I have the great fortune to work in a Pei building every day," said Neal Katyal, former acting solicitor general of the United States. Katyal is a partner in the law firm Hogan Lovells, which is based out of the IM Pei-designed Columbia Square building in Washington DC.
"His loss is immeasurable," Katyal added.
RIBA President Ben Derbyshire also shared his tribute.
"IM Pei's prolific contribution to architecture spans the globe and two centuries. His life's work is represented across continents, gifting a series of modernist masterpieces to cities from Hong Kong and Paris to Colorado and latterly Souzhou, his childhood home," Derbyshire said.
"It is a rarity for one architect to have such a vast portfolio of exceptional international work, but he will be remembered for much more than the robust, geometrical yet elegantly civic architecture."
Main image courtesy of Pei Partnership Architects.