Danielle Jones has not been seen since June 2001
Workmen from the Blue Circle cement works in Springhead Road, Northfleet, north Kent, discovered the body on Friday morning.
The complex is about five miles from East Tilbury in Essex where Danielle disappeared nearly nine months ago while on her way to catch the school bus
That was the last time the 15-year-old was seen and her body has never been found.
Detectives searching for the teenager have been informed and a post-mortem examination is being carried out on Monday.
A spokesman for Kent Police said the death of the woman was being treated as suspicious, but it was "impossible to draw any conclusions at this stage".
Danielle's disappearance on 18 June 2001 prompted a huge public response with large numbers of locals turning out to help scour local heathland.
Her parents also took part in a number of witness appeals.
Her uncle Stuart Campbell is currently being held on remand charged with her murder.