The model is Sharam Diniz. (source)
The cover is shot by Mert Alas & Marcus Piggott with styling by Tonne Goodman. On her fourth Vogue US cover, Rihanna is wearing Tom Ford with hair and make up by Yusef Williams and Mark Carrasquillo. (source)
Click here to view last year cover featuring Serena Williams, here to view 2014 cover featuring Kanye West and Kim Kardashian, here to view 2014 cover featuring Michelle Obama, here to view 2012 cover featuring Jennifer Lopez, here for 2011 cover with Rihanna, and here for 2010 cover with Gisele Bundchen.
Inez Van Lamsweerde & Vinoodh Matadin photographed Ben Stiller for the two covers. He is wearing Tom Ford and Givenchy, styled by David Vandewal. (source)
Click here to view last year cover featuring Adam Driver, here to view 2014 cover featuring Nicholas Hoult, click here to view 2013 cover featuring Douglas Booth, here to view 2012 Spring cover with Tahar Rahim, here for 2011 cover with Kanye West, and here for 2010 cover with Nick Jonas.