The Gossip Girl actor wore matching black pants and button-up shirt under a light blue blazer, one of Plein's spring/summer 2013 looks.
Westwick also can be seen in the brand's fall/winter advertising campaign, shot by famed photographer Terry Richardson, reports WWD.
He will be celebrating his upcoming birthday when he turns 24 this week.
"It's my birthday on Wednesday and my mum will take me out for dinner," Westwick shared to WWD.
Gossip Girl ended its fifth season last month, and will return for its sixth and final season this fall.
Watch Ed Westwick talk about Gossip Girl below: