The force said that Faith Williams was last seen in Bristol last Monday (July 7) but has since been missing.
The teenager is described as having long dark curly hair.
An Essex Police spokesperson said: “Can you help us find 15-year-old Faith Williams? She’s gone missing and we need to make sure she’s safe as soon as possible.
“We believe she may be in the Brentwood area and also has connections to Ipswich, Kent, Bristol, as well as south and west London.”
Anyone who has seen Faith, or has any information about her whereabouts, has been asked to contact police by calling 999 and quoting reference MPD/4071/25.
