A team of 30 search volunteers have been combing an area where a missing student's belongings were found after police said there has not been a "single sighting" of him since his disappearance.
Victor Ivanelo, 21, a Russian student at the University of Surrey in Guildford, was last seen leaving a friend's home in Esher at 2am on Sunday morning.
On Wednesday evening, a team of 30 searchers combed an area where his bag was found along a bridleway in Woodstock Lane South, Chessington, by a horserider on Sunday morning at about 11.40am.
Police helicopters and search dogs were also used to help find the student.
Officers are also said to be continuing house to house enquiries and several teams are dedicated to carrying out specific investigations.
Surrey Police chief inspector of operations Amy Buffoni said: “There has not been a single sighting of Victor since the time he left the property in Esher and we are extremely concerned for his welfare.
“The lack of communication from him is unusual and out of character. We are committed to trying to locate Viktor and will extend our activities as widely as necessary.”
Officers said Mr Ivanelo had been spotted on CCTV at Clapham Junction station at 3.37pm on Saturday, February 25, the day before he disappeared.
He is believed to have travelled to Claygate station from here, and wearing a three quarter length green puffa jacket, headphones and was carrying a bag.
When he was last seen leaving his friend's house in Esher on Sunday morning, he had been wearing a grey formal jacket, blue jeans and smart shoes and was carrying a black over-the-shoulder Hugo Boss bag.
He was not wearing his glasses at the time.
Mr Ivanelo's permanent address is in south west London but he has student housing in Guildford. Officers said he has not been seen at either address since his disappearance.
Chief inspector Buffoni said: “Please call us immediately if you have seen or have any information about the whereabouts of Victor.
“You may hold a single detail which you may think is unimportant but please share it could be vital to finding Victor safe and well.”
Mr Ivanelo's family, who flew to the UK from Russia on Monday, have hired private detective Andy Kemp to assist with the investigation.
Anyone with information should call Surrey Police on 101 quoting reference 45170020251.