Police are “very worried” for the safety of a 16-year-old girl a month on from her disappearance.

The investigation has been declared a “critical incident” after CCTV footage captured the moment Pamela Horvathova walked out of The Sheffield College at 2.07pm on December 18.

Detectives believe she walked to the city centre, and there was another sighting of Pamela at the iceSheffield arena the following day.

Superintendent Paul McCurry, from South Yorkshire Police, said the teenager, who is from the Slovakian Roma community, does not have a mobile phone or any presence on social media.

He told reporters Pamela’s family are “very upset” but community members have told police Pamela may not want to go home.

Officers are widening their search beyond Sheffield to the rest of the country and Europe, although police have no evidence she has gone abroad.

Asked how worried he was for her safety, Mr McCurry, said: “I think it’s fair to say we are very worried. This is a critical incident, we have a lot off staff involved in this.

Missing Pamela HorvathovaAngela Foulkes, chief executive and principal of The Sheffield College, and Superintendent Paul McCurry, appeal for help (Danny Lawson/PA)

“We need information from the public – sightings, any lines of inquiry we will follow.”

Officers are trawling through CCTV footage, which has allowed them to trace Pamela’s movements from the college, which she started attending in September, to Sheffield city centre on December 18.

“She is a very private person. Therefore we are trying to build a picture of what did Pamela like, where did she like to go, who is she friendly with etc,” said Mr McCurry.

“If Pamela is watching this, we just want you to come home.”