Ella has been located safe and well.
Mandurah Police have welfare concerns for 18-year-old Ella.
Police say Ella was last believed to be in the Secret Harbour Beach area about 6:00pm, on Saturday.
She is described as having tanned complexion, 163 centimetres tall, a slim build, long straight black hair, tied in a ponytail with hair extension and was last seen wearing a dark purple coloured dress, with skinny straps.
Police urge anyone who may of seen Ella or has any information on her whereabouts to contact them on 131444 and Reference number 777298.