Girls as young as 13 are posting explicit photographs on Facebook to "advertise" themselves to older gang members, police say.

The children, who are often already involved on the periphery of street gangs, are putting up highly sexualised pictures, apparently in an attempt to gain status.

Detective Chief Inspector Petrina Cribb, who leads a gang prevention programme for the Metropolitan police, said: "Some of the things you see on Facebook are just horrendous – very young girls posting pictures of themselves with very little on. We are talking about really, really inappropriate images of very young girls."

There is growing concern at the sexual exploitation of girls by street gangs. Last week the government announced £1.2m of funding to help girls involved with gangs who are raped or abused, with the equalities minister, Lynne Featherstone, describing the violence young women face as shocking.

While male gang members have posted videos and pictures online, often posing with weapons or boasting about their activity, for several years, Cribb, whose Heart Programme supports youngsters at risk of becoming involved in gangs, said the problem of young girls sharing explicit pictures of themselves online was not as widely known.

"You have very young girls putting inappropriate pictures of themselves – often of sexual poses and inappropriately dressed – that is associated with this gang phenomena," she said.

Girls who have been involved in street gangs have told the Guardian how sexual favours are regularly swapped for drugs and how many young teenagers are trapped in abusive relationships – sometimes with more than one male gang member.

Cribb said it was a familiar pattern. "Young girls tend not to be in the gang as such, they tend to be more on the periphery. They may hide firearms or deal drugs for the gang members but often they are being coerced or manipulated or pressurised into this activity or quite often feel that is just the way life is, they don't really realise it is not like that for everybody."

Cribb said that despite their involvement in often very serious criminal activity, these girls should also be recognised as victims.

"I think the public sees it as quite polarised: there are the people who are offenders and they are in gangs and then there are the people who are victims who are victimised by gangs. But the reality I see is that quite often they are the two sides of the same coin."

She said it was not just "bad kids" joining gangs, but often children in very challenging situations who made what they believed to be a "rational choice" to become involved. "It is kids who are under a lot of pressure who are often just trying to survive and what we need to do is provide them with the information and support to make them see that, although it may seem like the rational thing to do, it is incredibly dangerous and destructive."

The Heart Programme is run by experienced youth workers and focuses on reducing the risk of young people committing, and or being subjected to, violence, particularly sexual violence.

Hundreds of school pupils in three London boroughs are being offered workshops conducted by the charity Foundation 4 Life – some of whose youth workers are former gang members.

Cribb said it was crucial that such projects were on hand to offer support to vulnerable young people to help them find a different route through their teenage years.

"When you hear the stories of these young girls you never stop thinking this is a life ruined and it is such a dreadful, dreadful waste.

"We need to get in at an early enough age to try and correct these skewed ideas and make them realise they do have a choice and they do have rights and it does not need to be this way."

Last week, Scotland Yard announced an initiative to tackle gang crime in the capital with Trident – the Met unit that has worked to boost community confidence in the police and generate information about gun criminals – spearheading a new "gang command".

The Met said that since its launch there have been 515 gang-related arrests in a three-day operation last week and a huge amounts of weapons, drugs and cash seized.

A spokesman said more than half of those arrested have been charged with a variety of offences ranging from GBH and possession of firearms to violent disorder and assault.