Specialist police divers have been deployed to search for clues in the disappearance of Richard Okorogheye.
Mr Okorogheye left his family home on the evening of 22 March in Ladbroke Grove, west London. The 19-year-old Oxford Brookes student was reported missing two days later.
The underwater investigators were seen in one of the bodies of water in Epping Forest, with the teenager having last been seen in CCTV footage recorded nearby.
Mr Okorogheye, who has sickle cell disease and is said to have been struggling with shielding during lockdown, was seen in the footage after taking a taxi to Loughton, Essex, in the early hours of Tuesday 23 March.
A Metropolitan Police spokesperson said the search of the woodland continued for a fourth day on Sunday, but that nothing of relevance to the investigation had been found.
Initial inquiries found that Mr Okorogheye left his home in west London at around 8.30pm on 22 March. He was then seen boarding a number 23 bus heading southbound at around 8.44pm.
CCTV footage showed him in all black with a black satchel bag.
The Met released a statement saying that he took a taxi from the W2 postcode area to Loughton, 14 miles away from where he lives.
More CCTV showed Mr Okorogheye walking along Smarts Lane, Loughton, towards Epping Forest at 12.39am on Tuesday 23 March.
Detective Superintendent Danny Gosling said: “People can go missing from home for any number of reasons. Our job is not to cast judgement but to work to find them and bring them home safely.
“My message to Richard is clear. Our only concern is your safety. You are not in trouble and have done nothing wrong.
“If you read or hear this message we would ask you to contact us, or someone you trust, to let us know you are safe.
“Your loved ones and many other people who you do not even know, are very concerned.”
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He continued: “I would also like to thank the public for their continued support in sharing our appeals, checking doorbell and dash cam footage and passing on any information.
“As our efforts to find Richard continue, the eyes and ears of ordinary members of the public will be essential tools in our search.”
Anyone with information is asked to call police on 101 quoting 21MIS008134.