A pair of moped-riding muggers have robbed 15 youngsters at knifepoint in less than two weeks.

The duo have targeted teenagers across Bristol, South Gloucestershire, Bath and North East Somerset.

Boys as young as 13 have been threatened and forced to hand over mobile phones, wallets, jewellery.

The string of robberies began at 2200 BST on Thursday 10 April in Scotland Lane, Stockwood when three 16-year-olds boys had mobile phones and jewellery stolen at knifepoint.

Knife threats

How to avoid mobile phone theft Mark your mobile phone inside and out with your home postcode Make a note of your phone's SIM card number, serial number, telephone number and International Mobile Equipment Identity (IMEI) number (dial *#06# to find this out) Keep your phone charged, in credit and out of sight Stay with friends - but don't be complacent just because you're in a group Don't carry more cash than you need when you go out Always be aware of what's going on around you

On the same night, a 13-year-old was targeted in Keynsham Road, Willsbridge. His wallet was taken.

Over the next two weeks a further 11 teenagers were robbed in the Kingswood, Knowle, Stoke Bishop and Longwell Green areas.

In all cases the robbers were said to be two young men on a dark-coloured 50cc moped.

Both were described as black, in their late teens and wearing balaclavas under their crash helmets.

The rider is 6ft tall and 'lanky' while the pillion passenger is said to be about 5ft 6inches tall and stocky.

Anyone with information about the robberies is asked to contact the police or Crimestoppers.

Officers investigating the thefts are mounting extra patrols in areas where young people are known to congregate, and warning people to be on their guard.