The parents of a missing 11-year-old girl said they were in a "state of shock" as police stepped up their search for her.
The girl left her home in Bolton, Greater Manchester, on Thursday and travelled to London by train overnight.
Her parents urged her to let them know she was OK.
"We miss you, we want you to come home. We want to at least know you're safe. You're not in any trouble. Please contact us or the police," they said.
"We are in a state of shock. We want to know where she is, who she's with, but most of all, that she's safe. Please come home."
The girl left home without her parents' knowledge and travelled to Bolton railway station, arriving at 20:20 BST.
She then came into contact with an unknown man and woman, who were believed to be worried about her, and travelled on the same train as her to Manchester Piccadilly, police have said.
She was then seen boarding a train from Manchester Piccadilly at 21:27 to Birmingham New Street before getting onto another train at 23:10 to London Euston, arriving at 01:13.
She left Euston station alone and went onto Eversholt Street towards Euston Road at 01:17.
Police believe she was at London Bridge Tube Station at 11:16 and may be in the area around Tower Bridge.
The force is also looking to trace the man and woman, who travelled on the same train as her from Bolton to Manchester Piccadilly.
Detectives think they may know where the girl was going after arriving in London.
The child, who is of Ethiopian heritage and described as having a slim build, was last seen wearing a black Hijab with a blue headscarf and black dress.
Police say the woman, who is described as black, of slim build, was wearing a light blue tunic, black pants and black trainers with a white sole.
The woman's face was covered with a white face mask and she was carrying an orange carrier bag.
Det Ch Insp Paul Rollinson said: "We are understandably extremely concerned about the welfare of this young girl who was reported missing to us last night as it would seem extremely out of character."
He added that she may have travelled to the city to pursue her ambition of setting up a clothing business near Tower Bridge or to go sightseeing.
Police said the child had not spoken to friends or family about her plans to catch a train to the capital.