Samantha Parnell, who is 15, has been missing from her home near Bridgwater since last Saturday OCT 31.
She was last seen that day at Brean Leisure Park, near Weston-super-Mare, at 9.45pm.
At 10pm on Monday, she is thought to have called police from a public pay phone at the junction of Victoria Street and Mitchell Lane in Bristol city centre but was gone by the time officers arrived.
They are now urging her to contact them again to let them know she is safe and well.
Samantha is white, of medium build and 5ft 3in tall, with very long dark brown hair with orange tips and a fringe.
She is believed to have been wearing either a long-sleeved top with lots of zips, black leggings and black heel boots, or a black, white and grey long dress. She was carrying a pink cloth shoulder bag.
Samantha has links to Frampton Cotterell and police believe she may have gone there.
Anyone with information on her whereabouts should contact police in Burnham on 0845 456 7000, or call Crimestoppers on 0800 555 111.