A kiwi living in Western Australia has been missing for more than a week after disappearing during a night out in Perth.

Western Australia police are after sightings of Sean David Mitchell.

The 37-year-old from Rotorua, who has been working as a miner in Western Australia, was last seen drinking with friends at a beer cafe in Perth on Friday May 20.

He is also understood to have later boarded a yacht.

It is believed Mitchell used his Smart Rider card to board public transport at 9 that night, but he did not tag off.

An hour later he called a friend and spoke to her about going on another friend's yacht moored on the Swan River.

Four days later a member of the public told police he had found a bag belonging to Mitchell, and with some of his belongings still inside, on May 21, in the Swan River.

A police spokeswoman said the yacht and dinghy had been forensically examined but no clues to Mitchell's disappearance found.