(written from a Production point of view)
Carla Lewis is a casting director who hired background performers for Star Trek.   She is the co-founder of Hollywood Operating Systems (or Hollywood OS) and is currently the head of Headquarters Casting, "a full service principal and background talent casting agency."  In February 2012, Lewis and Headquarters Casting have open casting calls for background performers for the Star Trek Into Darkness. 
Lewis has also cast background performers for such films as Lords of Dogtown, Failure to Launch, The Fast and the Furious: Tokyo Drift, Knocked Up, and Georgia Rule. She recently wrapped up work on National Treasure: Book of Secrets. In addition to Star Trek, she is casting extras for Ben Stiller's Tropic Thunder and the upcoming ABC series Miss/Guided. She also continues to work as casting director on Jimmy Kimmel Live!
Webster (and Headquarters Casting) oversaw an open casting call for extras for Star Trek at the Hollywood OS office in Burbank, California on 10 November 2007. They were looking for people to play Vulcans and cadets. They are seeking "thin, athletic men and women, ages 18-90", particularly those with "interesting and unique facial features."  Hundreds of people – both fans and actors just looking for work – attended the casting call.