Family, friends and classmates of the four-year-old gathered at St Mary Star of the Sea Parish Church in support of her mum, Ellie Smith, and stepfather, Jake Gliddon.
It has been nearly two weeks since the girl went missing at the Blowholes campsite.
The search is now a global operation, as international partners including the FBI are brought in on the investigation.
“In any operation of this scale, we reach out to police forces not only across Australia but indeed across the world,” WA Commissioner of Police Chris Dawson said.
Police have received more than 200 calls about the girl but none have so far led them to the child.
Superintendent Ron Wilde said while calls about possible sightings had proven “unfruitful” so far, he encouraged the public to keep sharing information
“We’re very grateful for that,” he said.
“We still want the public to come forward, give us information, which we can follow through.”
Most of the campers who were at the Blowholes campsite on that fateful night have been tracked down and interviewed.
But with no developments on the mystery car spotted driving away from the campsite in the early hours of October 16, police are keeping an open mind.
“We have a very motivated team and I’m very hopeful and confident that we will resolve what happened to Cleo,” Superintendent Wilde said.