A missing boy had been in the water with four others near Lechlade on Thames, Gloucestershire, when officers were called at around 10pm last night.
The boy was swimming with friends near Lechlade on Thames when he went missing.
His friends jumped in to try and find him before getting out of the water when emergency services arrived.
The river bank have been closed as part of the search.
Local authorities have also urged members of the public to avoid the area while the search continues.
A spokesman from Gloucestershire Fire and Rescue Service said: ‘We were called at 10.03pm by the coast guard to reports that some teenagers believed to be aged about 17, had been playing in the river at Lechlade and one hadn’t resurfaced.
‘We assisted the search by sending three crews from Fairford, Gloucester South and Tewkesbury, along with boat crews.
‘We liaised with coast guard and the police, who were co-ordinating the search, and came away from the scene at about 4am.’
A Gloucestershire Police spokesperson said: ‘Searches have been taking place in the River Thames after a report a teenager was in the water near Lechlade on Thames.
‘Police were called at around 10pm yesterday (Sunday 30 April) and emergency services attended.
‘Officers have been supported by the National Police Air Service, Gloucestershire Fire and Rescue Service and Severn Area Rescue Association while searches continued into the early hours of this morning (Monday).
‘The teenage boy has not yet been located, and specialist search teams will be continuing with the search today (Monday). His next of kin are aware.’
