The 51-year-old actress was spotted with the newlyweds in the tropical locale after serving as maid of honor in their surprise wedding Wednesday. The couple also brought along TV personality Chelsea Handler and actor Jason Bateman and his wife Amanda.
Aniston and Theroux married at their Los Angeles home in front of 70-plus guests, including Lisa Kudrow and Ellen DeGeneres. The couple reportedly told family and friends the party was to celebrate the actor's 43rd birthday to keep the ceremony secret.
The pair have been together since 2011, and confirmed their engagement in August 2012. Aniston was previously married to actor Brad Pitt from 2000 to 2005, while Theroux was involved with stylist Heidi Bivens from 1997 to 2011.
The actress and Cox portrayed Rachel Green and Monica Geller, respectively, on 10 seasons of NBC sitcom Friends. Cox and ex-husband David Arquette share one daughter, 11-year-old Coco, and the 51-year-old star is currently engaged to Johnny McDaid.