The young man was last seen at around 5pm at Church Ope Cove wearing a dark-coloured wetsuit. He was reported as missing at around 7.37pm.
Portland coastguard rescue team, two RNLI lifeboats from Weymouth, an RNLI lifeboat from Swanage and the coastguard rescue helicopter from Lee-on-Solent have been sent. A Royal Navy helicopter, two Royal Navy warships, a police helicopter and Dorset police are also involved in the search.
Any member of the public who was in the area at the time and has any information which might aid the search is asked to contact Solent coastguard operations centre on 02392 552100.
