15-year-old Andreea was last seen on Friday, 1 October at her home in Canterbury, Kent.
Her cousin, 16-year-old Izabela, was last seen on Sunday, 3 October in Harrow, west London.
A high risk missing person investigation has been launched and officers are pursuing a number of lines of enquiry in an effort to locate the two girls.
In addition to London and Kent, they are believed to have links to Leicester and Dundee. Officers from Police Scotland are assisting officers from the Metropolitan Police with their investigation.
On Tuesday, 5 October a 54-year-old man was arrested on suspicion of people trafficking and remains in custody at a north London police station.
Detective Chief Inspector Tony Bellis, of the North West Public Protection Unit, said: “We are becoming increasingly concerned for the safety of Andreea and Izabela.
“While we are keeping an open mind as to their whereabouts, we believe they may have been taken outside London by people who could do them harm.
“I would like to appeal directly to Andreea and Izabela. You are not in trouble and there are people who want to help you. Please contact the police or someone you trust when it is safe to do so.
“I would also urge members of the public, particularly in London and Dundee, to come forward if they have any information that could help us.”
Anyone who sees the girls should call 999. Anyone with other information about their whereabouts should call 101, giving the reference CAD7399/06OCT.
Information can also be provided to Crimestoppers, anonymously, by calling 0800 555 111 or by visiting www.crimestoppers-uk.org
