Donna S

Donna S was an employee of Miss Kizlet whose Foursquare was found by Clara Oswald using face-match. According to her page, Donna also had a Facebook, and had had 17 check-ins. She used this information to discover where Kizlet's offices were. (TV: The Bells of Saint John)

Behind the scenes
Although just off screen, the rest of Donna's surname is Shakesheff, and she was the art department co-ordinator for the episode.