'You look good but I'm worried. You've lost so much weight!' wrote one fan.
‘Whoa she is so skinny now,’ wrote another fan.
Just last week Keira showed off her figure in an Instagram post where she is seen sporting a bright pink bikini.
'Weekend vibes - this bikini gives me life,' she captioned the photo.
In September, Maguire announced she had split with her ex-boyfriend, vineyard manager Jarrod Woodgate.