Alison and Tim Hysom joined Detective Inspector John Delaney at Ilford police station to appeal for the public's help in finding their 15-year-old daughter.
DI Delaney added: "We are taking this matter seriously and a lot of resources, including search teams, have been deployed. We are concerned for her welfare because she is vulnerable, she is suffering from depression and she is just 15.
"It is out of character and there has been no contact from her since the day she went missing."
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A lamp in the tower which houses Big Ben is to be switched off for the first time in more than 70 years.
Sir Bruce entertained audiences for more than seven decades.
Work in the tower will also pause over the bank holiday weekend.