In connection with the disappearance of a student who was last seen on Boxing Day, a man was arrested.
Joy Morgan, reported missing to the police on February 7, was last seen in Ilford, East London.
A 40-year-old man from London has since been arrested and released on bail. Further investigations are pending.
Officers described the case as a "complex investigation of missing persons".
The 21-year-old student from Hertfordshire University in Hatfield is described as black. She is slim, 5 feet 5 inches tall and has Afro hairstyle that she often wears with a scarf.
She also wears glasses.
Her family requested an appeal: "We love you, we miss you, wherever you are, write or call, so we know you're alright.
"It does not matter what happened, just come home."
It was Morgan's 21st birthday on Tuesday.
It has connections throughout London, including Battersea and Cricklewood, as well as Bedfordshire.
Welwyn Hatfield Chief Inspector Tannis Perks said, "This is a complex investigation of the missing person, and we are working hard to determine the circumstances surrounding the disappearance of Joy.
"Understandably, her family is very worried about her and desperately wants to know she's fine, and I want Joy to contact us to let her know she's safe."
Anyone with information should call the police at 101. Immediate sightings should be reported over 999.