Detective Chief Inspector Mike Ashcroft said: "Although we can't categorically prove that Mark is dead at this time, we are treating this as seriously as we can.
"His sudden disappearance is completely out of character. He is close to his family but they have not heard from him at all.
"He hasn't used his mobile phone, or carried out any financial transactions, hasn't turned up for pre-arranged appointments and meetings and there has no been no reported sightings of him.
"There were no signs that he was depressed or may wish to harm himself. He seems to have vanished."
Mark is described as white, 5' 9", clean shaven, with a tanned complexion and of stocky build. He has blue eyes and is bald.
Ring police on 101 or email firstname.lastname@example.org quoting Operation Light or contact the independent charity Crimestoppers anonymously on 0800 555111.
Russell Manning appeals for help in finding his brother Mark who has not been seen since April.
The brother of missing Sussex Mark Manning has made a heartfelt plea to him to get in touch.
Russell Manning appeared at police press conference in Worthing today where he read a statement which appealed for information about his missing brother.
Police have launched a murder investigation into the disappearance of Mark who lives in Lancing.
Detectives from the Surrey and Sussex Major Crime Team are now investigating after Mark, 54, of Brighton Road, was reported missing on April 22.
DC Andy Hobden said: "The man who came into the shop is described as around 6', stocky or muscular build, about 30 with a local accent. He was wearing a woolly hat pulled down over his eyes with holes cut in it for his eyes. He wearing dark clothes and black gloves.
"This was still a fairly busy time of the day and we are sure someone must have seen this man as he went into the shop. If you have any information or saw anything suspicious in the area please contact us on 101 quoting serial 1463 of 18/2."
Police are appealing for witnesses to a robbery at a betting shop in Lancing.
At around 8.30pm on Tuesday, February 20, a man walked into the Ladbrokes on South Street and demanded money from the member of staff.
Around £700 was handed over and the man left bumping into a person outside.
It is thought that a second male was waiting outside and they both ran south along South Street and turned right into Elm Grove.
Two teenagers missing from their Lancing homes for three days have been found safe and well.
The girls, Jaadine Hobden and Jaydeene Boarer, both aged 13, went missing on 3rd February 2014 but were found yesterday.
Police would like to thank the public and media for their assistance.
Police are concerned for the welfare of two 13-year-old friends who have been missing from their Lancing homes for three days.
The girls, Jaadine Hobden and Jaydeene Boarer, went missing on 3 February.
Jaadine, from Hurstfield, went missing after school and she is believed with Jaydeene Boarer, 13, of Derek Road, who is also missing.
PC Roisin Vafaee said: "We are increasingly concerned for the two girls because of their age and the amount of time they have been missing.
There has been sightings of them in Portslade, Lancing and Worthing. We would urge the girls to contact us to say they are OK."
An 86-year-old Lancing man has died following a crash with a parked van in Freshbrook Road, Lancing at around 3.45pm on Monday 5th August. He has been named as Donald Spooner of Brookway, Lancing.
Mr Spooner was riding an electrically powered pedal cycle at the time of the collision. He was taken by air ambulance to the Royal London Hospital with a critical head injury, but sadly died later that night.
His next of kin have been informed.
Modelzone the country's largest specialist toy and model chain has gone into administration.
The company which is based in Lancing, Sussex has 47 shops across the UK.
Four hundred workers are at risk of losing their jobs.
Bill Freeman of the Lancing Manor Residents' Network speaks about local flooding.