Pertti Rantaniitty (50) is still missing from Sleipner A in the North Sea.
The search for the welder, who works for ABB Offshore Systems, will continue through the evening.
A Finnish national, Mr Rantaniitty lives in Skudeneshavn north of Stavanger.
He was last seen at work at 13.30 on 22 February. Colleagues became concerned when he failed to show up for the coffee break at 15.00.
The alarm was sounded at 16.30, and a search was launched on the platform as well as by air and sea.
Mr Rantaniitty has worked for ABB since 1990 and is described as an experienced offshore worker.