Sixteen people have fallen prey to mobile phone thieves in Brighton in the past week.
The victims were usually talking on their phones when the offenders struck.
The thieves sneaked up behind, grabbed the phones and ran.
Most thefts happened outside entertainment venues in the city, including clubs and cinemas.
One 14-year-old boy lost his phone while making a call outside the Odeon in West Street, Brighton, at 4.10pm yesterday.
Thieves also targeted people leaving clubs in the Kings Road Arches on Brighton seafront while they were calling taxis.
Most victims are male and in their late teens or early 20s.
Hot spots for the crime are Kings Road, Queen's Square, Trafalgar Street, St James's Street, the Palace Pier and London Road areas of Brighton.
The thieves work in pairs and pounce quickly. Victims have been able to offer only vague descriptions of the offenders.
So far no violence has been used.
Detective Inspector Paul Fullwood, of Brighton CID, warned the thieves: "We've had four-year sentences handed down to mobile phone thieves caught in Brighton in recent weeks."
Police have launched an undercover operation to target suspects.
Mr Fullwood said: "Members of the public should be on their guard when they talk on their phones and not clip them to bags or belts where they can be seen and stolen."
The Odeon offender had ginger hair and wore a white jacket.
Anyone with information should contact Inspector Julie Wakeford on 0845 6070999.
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