They stare out from the screen: brazen, menacing, occasionally risible, but always brandishing a serious weapon. These young people armed with guns, knives and machetes make little or no attempt to disguise themselves. Their images were all found during just one morning's trawl across social networking sites such as Bebo. Together they present an army of reasons why the Government is struggling to tackle violent youth crime.

The Home Secretary, Jacqui Smith, is about to announce new tactics – which will include taking young men and women convicted of carrying knives to the A&E department of their local hospital to see what stab wounds are really like. They will also meet the families of those who have been maimed or killed to see the grief and pain such attacks can cause.

Last week was the worst so far this year for knife crime. Nine people died, eight of them on Thursday or Friday. Some of their names were released yesterday. Melvin Bryan was knifed in the neck and chest at a bedsit in Edmonton, north London. He was 18 years old. Not far away, in a squat on Tottenham High Road, 42-year-old Gennar Jaronis was found dead. Adnan Patel died after being chased and knifed by a gang in Leyton, east London. He was 20. The police continue to make arrests: yesterday Sarah Anderson, of Bellenden Road, Peckham, was remanded in custody at Greenwich Magistrates' Court, charged with the murder of Dee Wills outside a supermarket in Peckham on 1 July.

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The lengthening list of victims has provoked the Government into promising new and more dramatic intervention. But Professor Ellis Cashmore, an expert on consumer culture, believes these measures may be in vain. The problem is rooted, he says, not in policing but in the new status of knives as "bling" for those who can't afford gold chains and fast cars. "The knife has almost been stripped of its instrumental purpose, which is to cut things, and instead people are posing with them because it suggests to others they have status and it is as important as having a new pair of trainers or jewellery," he said. Websites are crucial to this. "They can't walk down the street carrying them, so the internet provides a theatrical setting to display their weapons. It is also saying to others, 'I'm a person to respect, a person of honour in my sub-set.'"

Professor Cashmore, of Staffordshire University, said the knife-crime epidemic was being fed by the media's reporting of it. "The copycat effect is very powerful. There is a buzz and awareness of what is going on," he said. "The reason the posing spills into violence is because it becomes a badge of honour within the tribe or group if you have stabbed someone and the others have not. Everyone has to earn their stripes. There are some problems for which there are no practical solutions. I don't think tougher sentences are a practical solution to the problem, no matter what Jacqui Smith says."

The selection of pictures on Bebo yesterday showed this culture at its worst. One showed two teenagers under the heading "Snub Blaxk Ea5t5ide Grove Boy" brandishing a shotgun, while another, under "Tommy Solly", showed a young man with a 2ft machete.

David Wilson, a professor of criminology at Birmingham City University, said one cause of the problem was distrust between young people and adults. "They feel they have been dismissed by adult society as chavs, hoodies and feral youth, and they are responding to that by taking matters into their own hands," he said. "Some people are carrying knives because they are scared, but a smaller group is carrying them for symbolic reasons. It is about being a man, gaining respect and saying I am an adult and I can take care of myself."

One of the youngest victims to lose his life so far is David Idowu, 14. He died on Monday, three weeks after being stabbed in south London. An argument on a football pitch in Borough escalated into murder when David was chased and then stabbed. One theory is that the argument began because of rivalry between pupils at Walworth Academy in Southwark, where David studied, and another school.

Friends and family of the murdered teenager will march through London in a protest against knives on Saturday 19 July, at midday, starting at the spot where the stabbing took place in Great Dover Street.

Those who knew David described him as deeply religious and a model pupil. His parents, Tim and Grace Idowu, believe their son is now with God. Odunayo Otti, a church elder at the Christ Apostolic Church in Bermondsey, where the Idowu family worships, said the Government had let knife crime get out of control. "They ignored it because they thought it was a black-on-black thing when they should have been doing something about it before it got out of hand," he said.

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"If you look at this in a Christian way, maybe a demon has got hold of the youth. The community needs to turn to God." He supported much tougher sentences for carrying a knife, he said. "Young people and parents need to take responsibility for themselves. A single life lost from knives is too much to bear – let alone four in one day, as we saw on Thursday."

Online images...

Shakilus Townsend, 16

Murdered by a gang on 3 July. Pictured posing with a knife near his home in Deptford, south-east London.

S Rillz Man Dem

A teenager from the gang holds a hunting knife and makes no attempt to disguise himself.

Tommy Solly

Wearing a deadpan expression, he wields a three-foot machete with a notched blade.

Southside Blood Thugz

A masked teenager with his gang's name on his sweatshirt holds a rusty machete.

Vernon Chapman

Calls himself Jay Da Bad Azz. He stands in motorcycle leathers holding a handgun.

General Yung Depoh 'Bad Man Killer'

He sits in a bedroom and holds a handgun while staring at the floor.

Snub Blaxk Ea5t5ide GroveBoy

One teenager holds a shotgun, the other poses with a shotgun shell.

Slim The Immaculate

He wears a hood and bandana to cover his features while standing outside a house with a handgun.

Neasdens Most Wanted

The teenager apes the horror film genre by wearing the 'Scream' mask and holding a kitchen knife.

Liam K

He stands against a grubby wall wielding a curved scimitar-style sword and a long curved knife.