Arlene Arkinson, 15, from Castlederg, went missing after a disco in Bundoran in 1994. Her body has never been found.
The inquest was due to go ahead this autumn but a hearing today was told that a “huge amount” of outstanding paperwork still has to be re-examined by police officers.
The police files on the murder run to 3,016 documents and 793 witness statements.
A lawyer for the police said the workload already facing the unit meant the process of studying the case notes was not set to start until the autumn and could take four months.
He said they must then go through all those papers to assess their relevance before passing them to legal representatives of both Robert Howard – the child killer who was acquitted of Arlene’s murder in 2005 – and the Arkinson family for examination.
The Arkinson family lawyer, Ivor McAteer, said it was likely this would take the coroner four months, and the lawyers would then need a similar timeframe to consider the documents.
John Leckey agreed that the inquest would not happen this year, and said there was also “a question mark about next year”.
Transcripts and depositions from Howard’s murder trial in 2005 and files relating to the murder of Hanna Williams are also due to be given to the coroner.
Howard is currently serving a life sentence for the rape and murder of the 14-year-old, from Deptford, south London, whose body was found in a cement works in Northfleet, Kent, in March 2002.