Concern for a teenager is growing after he disappeared in mysterious circumstances a week ago.

Robert Francis, 19, vanished from his home in New England Street, Brighton, on March 16 after telling his family he was going out with a friend.

His family is "frantic with worry" and his mother, Linda, yesterday made a heartfelt plea for him to get in touch and return home.

Police have described his disappearance as a "complete mystery" and Mrs Francis said there had been no rows or arguments in the family.

She said: "There was no reason why he went missing - no rows, or any trouble which would make me think he would go missing."

Robert's three sisters Christine, Katie and Lisa have also asked for help in tracking down their brother - a Manchester United and Playstation fan who they said would help anyone.

Robert left his terraced home at about 8.30am after a friend knocked on the front door.

By Friday he had still not returned and his family alerted the police.

A tearful Mrs Francis said: "Normally if he goes out and stays out he will ring to tell me and even if he stays out all night he will be back in the morning and will apologise for being out.

"It really isn't like him to completely disappear."

The family has distant relatives in Suffolk but they do not believe he is with them.

It is understood Robert attempted to cash a Giro cheque in the run-up to his disappearance but was unable to.

Robert has lived in Brighton all of his life and knows the area well.

His family said he had not been involved in any trouble.

Brighton and Hove police have issued a statement appealing for help.

Sergeant Martin Drabble said: "Robert's disappearance is a complete mystery. It is totally out of character for Robert not to contact his family and friends for such a long time.

"He has not been missing before and he is not suffering from depression. We urgently need members of the public to contact us if they think they have seen him since last Thursday. His family are frantic with worry."

Robert is understood to have been wearing a navy blue Nike jacket and trainers. He is 5ft 8ins tall and of thin build with short brown hair and blue eyes.

Police believe he may have access to some money but does not have a mobile phone.

Mrs Francis said: "We just really want him to get in touch or for anyone who has seen him to get in touch.

"We just want him back with us."

Anyone with information is asked to contact Sussex Police on 0845 6070999.