The mother of missing four-year-old described how the past few days had been "horrendous".
Cleo Smith was last seen sleeping in her family's tent at the Quobba Blowholes coastal camp in Western Australia early on Saturday morning.
Her mother said she discovered the tent open later that morning and the girl missing, along with her sleeping bag.
Teams are searching by air and sea.
Cleo's mother, Ellie Smith at an emotional news conference said: "We haven't really slept."
"Everyone asks us what we need and all we need is our little girl home... The worst part is, we can't do anything more. It's out of our hands so we feel hopeless and out of control."
Cleo's family travelled to the remote site, about 900km north of Perth, at the weekend for a camping trip.
The Quobba Blowhole site, in Macleod, is a local attraction on the state's Coral Coast - known for its windswept ocean scenery, sea caves and lagoons.
Ms Smith said she had put Cleo to sleep after dinner on Friday night, seeing her again at 01:30 when she woke up asking for water.
Cleo was sleeping on an air mattress next to her younger sister's cot, in a separate room of the family's tent, Ms Smith said.
She saw the tent open and Cleo gone at 06:00 when she went to give her youngest daughter a bottle, she added.
"We went looking, trekking, making sure she wasn't around the tent," Ms Smith said.
"Then we got in the car and started driving around everywhere... We realised we had to call the cops because she wasn't here."
Police said they had initially focused their search on a row of shacks near the coastline, adding that bad weather had hampered their efforts.