Jonathan Larsen, the former regional managing partner at DTZ/Cassidy Turley’s downtown L.A. office, has assumed the role of managing director and principal at Avison Young.

In his new role, Larsen, 55, will be responsible for growing the firm’s business in its West L.A., San Fernando Valley and Ventura offices. He started last week.

“I had actually talked to them three, four years ago, before they opened up here,” Larsen said. “I made the decision to go to Cassidy Turley to open their practice.”

Larsen opened Cassidy Turley’s office in April 2012 and brokered a number of large leases and sales downtown, most recently last year’s biggest office lease, representing Lewis Brisbois Bisgaard & Smith in its December deal for 215,000 square feet at the U.S. Bank Tower after its offices were severely damaged in the DaVinci fire. He left the firm Jan. 23 after a shakeup by new owner DTZ that saw 45 people nationwide pushed out.

DTZ purchased Cassidy Turley in a year-end deal valued at around $557 million. Larsen said he was Cassidy Turley’s largest shareholder on the West Coast.

“I talked to many, many firms,” Larsen said, following his departure. “I liked that (Avison Young) was privately held, continued to hire the best in the market and they were growing.”