Teenagers have been using messaging service WhatsApp to co-ordinate violent carjackings in Birmingham, police say.
Officers believe youths, often armed with knives and in some cases stun-guns, are behind a spate of robberies in the south of the city since October.
Raids were carried out earlier during which three 16-year-old boys were arrested, and cash, a car key, mobile phones and clothing were seized.
WhatsApp declined to comment on the specific case when asked by the BBC.
Police began investigating attacks in Moseley and Kings Heath, in February.
In some cases, drivers were left with minor burns after being shocked with stun-gun type devices, West Midlands Police said.
About 30 carjackings are being linked, with more than 20 people arrested - including a boy aged 13. One stun-gun has been recovered.
Police previously revealed their suspicion teenage boys were being "coerced" into committing carjackings.
Det Sgt Phil Poole said: "From the phones we have seen there's been a lot of discussion or pre-planning via social media.
"They are contacting each other via WhatsApp predominantly."
It is believed the group are also sharing screen shots of press coverage between themselves, "indicating they have got knowledge and awareness of those offences," he added.
Det Sgt Poole said the majority of offences had been committed around the Moseley and Kings Heath areas in south Birmingham, but others have taken place elsewhere in the city that police have said are not linked to the 30.
Sarah Khatri spoke of her fear when two men threatened her with a blade and stole her Kia outside St Columba Church in Chantry Road, Moseley, at about 09:45 GMT on 27 March.
Another victim was sitting in her Mercedes A-Class when a group of men - one wearing a mask - smashed her driver's side window with a baton outside her Grove Road home in Kings Heath, at about 22:00 on 19 March.
The 27-year-old, who does not want to be named, managed to escape and was uninjured, but left shaken and afraid.
"It's just awful," she added.
"When I was getting ready to go to bed I was convinced they were going to get into the garden and get me."
WhatsApp did not answer whether it would co-operate with West Midlands Police.
With a billion users worldwide, the company has said previously that protecting private communication is one of its "core beliefs".
WhatsApp's encryption system came under the spotlight after the Westminster terror attack.