Tamara Clarke was last seen wearing black shorts and a white T-shirt
Internet social networking sites are being examined by police searching for a missing 13-year-old girl.
Tamara Clark, known as Tammy, was last seen leaving the Barbican Leisure Park in Plymouth on Sunday evening.
She was caught on CCTV in the company of two youths and was seen heading in the direction of the city centre.
Her mother has appealed for her to come home and police said it was "entirely out of character" for the teenager to have disappeared.
Det Insp Jim Colwell of Devon and Cornwall Police said they were "very concerned" about Tamara.
"We do know Tamara used social network sites such as Bebo and messaging services such as MSN, clearly we've got an obligation to look at those as potential lines of enquiry."
Police are also searching the Barbican and Hooe areas of Plymouth and carrying out house-to-house enquiries.
They are also examining CCTV footage of the area where Tamara was last seen. Det Insp Colwell said: "There are a number of potential routes away from this site and it's going to be a very slow and painstaking process".
Tammy is 5ft 5in tall with long brown hair, normally worn in a ponytail.
She was last known to be wearing black shorts and a white T-shirt.
Anyone who has seen her or who may know of her whereabouts is asked to contact police.
Officers would also like to speak to the youths seen with Tammy in the CCTV images.
One is described as about 18 years old, wearing jeans, trainers and a blue or black hooded top with a collar.
The second youth is about 19 years old, 6ft tall and wearing grey three-quarter length trousers, sandals and a blue baseball cap with a white cross of St George on it.