After graduating, Ries moved to Silicon Valley in 2001 as a software engineer with There, Inc. He worked with the firm until the 2003 launch of its web-based 3D Virtual World product, There.com. The company soon failed.
In 2004, Ries left to join one of the founders of There.com, Will Harvey in co-founding IMVU Inc., a social network. IMVU investor Steve Blank insisted that IMVU executives audit Blank's class on entrepreneurship at UC Berkeley.
There Ries picked up Blank's method of fast customer feedback, which Blank called "customer development", and applied it at IMVU in combination with lean software development, testing alternate versions of the product and measuring download rates. IMVU deployed code to production nearly 50 times a day, an unusually rapid development cycle. Ries also copyedited an early version of Blank's book on customer development, The Four Steps to the Epiphany.
IMVU aimed to integrate instant messaging with the high revenue per customer of traditional video games. Ries and Harvey did not seek a large amount of initial funding and released a minimum viable product within six months. In 2006, the firm raised $1 million in its first round of venture fundraising from the Seraph Group, eventually raising an additional 18 million. In 2008 after a new CEO joined IMVU, Ries stepped down as CTO, remaining as a board observer.
Ries is also the author of The Startup Way, a book on modern entrepreneurial management.