Now 34, James Hirschfeld started Paperless Post with his elder sister, Alexa, because he had a problem planning his 21st-birthday party—a Bostonian, winter-defying, beach-party-themed bash. James realized it was too late to send invitations by mail, while e-mail felt too dry and informal. “I called my sister, and I was like, There needs to be a way of creating invitations that are as efficient as an e-mail,” but which would still have “the customization and beauty of printed ones.”

Since launching in 2009, Paperless Post has circulated millions of invitations and now employs 130 people. It’s the epitome of a disrupting tech start-up, but Hirschfeld, the C.E.O., describes it more as an art project. “I’ve never been that into computers,” he says from his office in Manhattan’s financial district. “Tech is more of a tool for me to share my love for beauty and design.” It lead him to partner with designers such as Oscar de la Renta, Kelly Wearstler, and John Derian.