I used to see Six Degrees threads on IMDb all the time, but never here. I'll start, and anyone who responds with the answer can post two random celebrities for the next challenge, etc.
Mackenzie Davis and Paz Vega
Mackenzie Davis was in Blade Runner 2049 with Jared Leto
Jared Leto was in Urban Legend with Alicia Witt
Alicia Witt was in Two Weeks Notice with Hugh Grant
Hugh Grant was in Music & Lyrics with Drew Barrymore
Drew Barrymore was in 50 First Dates with Adam Sandler
Adam Sandler was in Spanglish with Paz Vega
Drew Barrymore and Clark Gable
Clark Gable was in Gone with the Wind with Vivien Leigh
Vivien Leigh was in A Streetcar Named Desire with Marlon Brando
Marlon Brando was in The Island of Dr. Moreau with Val Kilmer
Val Kilmer was in Batman Forever with Drew Barrymore
Kristen Stewart and Will Smith