Search after man's bag found in Swan River

A land, sea and air search is being launched for a man who went missing five days ago and whose bag was found in Perth's Swan River.

Sean David Mitchell, 37, was last seen drinking with friends at a CBD pub at 5pm on Friday and called a friend about five hours later, telling her about plans to go on another friend's yacht.

He is believed to have used his Smart Rider card on a train about 9pm, but did not tag off.

His bag was found at Blackwall Reach in Bicton the next day, but the man who found it did not notify police until Tuesday night.

Family and friends have taken to Mr Mitchell's Facebook page to plead for information, with Renee San Martin writing she had called the hospitals and police had told her no boats were unaccounted for.

"We can't be sure he even got on one," she posted.

"We now know that he was at the Johnston St park when he phoned me at 10:15. Near the Freshwater Bay Yacht Club.

"I was there looking for him until 2am last night; showed security his photo but he does not remember seeing him Friday night and says nothing was happening there Friday but people securing boats."

On Friday night, Perth was bracing itself for a wild storm that also battered the South West region, leaving tens of thousands of homes without power, flooding roads and damaging property.

Friends have already been searching for Mr Mitchell in Bicton, including using a drone.