Police have named a missing 19-year-old woman who detectives fear has been murdered.
Hertfordshire Police are urgently seeking to trace 22-year-old Jack Wall in connection with the disappearance of Amelia Arnold, who was last seen on Wednesday.
Wall, of Hadrian's Walk, Stevenage, is being urged to hand himself in to police, who have also issued an appeal for sightings of a Citroen Berlingo van as part of their inquiry.
Detective Chief Inspector Tim Redfearn, from the joint Bedfordshire, Hertfordshire and Cambridgeshire Major Crime Unit, said: "We have reason to believe that the missing woman has been murdered and we'd urgently like to speak with Jack Wall in connection with the inquiry. It is likely he may be in the Stevenage area, but he could be further afield."
DCI Redfearn, who is leading the inquiry, added: "I would urge anyone who has information about his whereabouts to call police as a matter of urgency. I'd also like to appeal directly to Jack. If you are reading this, please go to Stevenage or your nearest police station to speak with officers."
As part of the inquiry, detectives and scene-of-crime specialists are examining a property in Hadrian's Walk. Witnesses who may have seen suspicious activity at the address between Wednesday and Friday are also being asked to come forward.
Mr Redfearn said: "We've been speaking with residents in Hadrian's Walk but I would like to hear from anyone who has been in the area between these times and believes they may have seen or heard any suspicious activity to make contact with police.
"We would also like to appeal to anyone who may have witnessed anyone acting suspiciously in a white Citroen Berlingo, registration R389 VDP, in the Stevenage area since Wednesday. Any information, however small could prove vital to our investigation."
Meanwhile, a 41-year-old man from the local area has been arrested in connection with the investigation and is in police custody.
Anyone with information which could assist the inquiry is asked to contact police immediately by calling the non-emergency number, 101 or information can be passed on anonymously to the Crimestoppers hotline on 0800 555111.