HM Coastguard, the RNLI and Dorset Police are continuing the search for David Haw.
Mr Haw, 24, was reported to have fallen overboard after his RIB collied with a navigation buoy in Poole Harbour early on Bank Holiday Monday.
Three people were reported to have been onboard the RIB.
Police received a report of the incident on Monday 2 May, and are asking for anyone with information of the incident to contact Dorset Police at www.dorset.police.uk, via email [email protected] or by calling 101, quoting occurrence number 55220068866.
Racing at the Poole Regatta, which had been taking place over the bank holiday weekend, was abandoned.
A Southampton man arrested earlier on suspicion of manslaughter has been released under investigation.