Cleo Smith was last seen by her parents about 1.30am on Saturday at the Blowholes campsite at Macleod, north of Carnarvon.
The girl was wearing a pink one-piece sleepsuit with a blue and yellow pattern. She was in a red and black sleeping bag which has since been reported missing.
Homicide and major crime forensic investigators are assisting local authorities.
Police on Monday searched a number of shacks located along the coastline at the campsite.
"We are continuing to throw everything we have at this and we will continue until we can provide some answers as to what has happened to Cleo," Inspector Jon Munday told reporters.
"Certainly we are not ruling (abduction) out. We are not going to get blinkered or assume that something has happened. Everything is on the table until we can rule it out."
A police helicopter and drones have also been deployed as part of an aerial search.
Inspector Munday would not comment on reports a car had been heard speeding from the campsite in the early hours of the morning.
He said the conditions near the tourist hotspot were difficult.
"Every hour that goes by with a four-year-old out in this environment, there's obviously limited water supply, it is warm, very limited shelter. It is very, very concerning," he said.
"That's why we do hold grave fears for Cleo at this time."
On Sunday, the girl's worried mother, Ellie Smith, took to social media also pleading for help.
"It's been over 24 hours since I last seen the sparkle in my little girl's eyes! Please help me find her," she posted.