The Missing Persons Bureau currently holds records of around 1,000 people who have not been identified, some dating back to the 1950s.
It will feature pictures of bodies, but any images deemed to be distressing will be marked with a warning and require confirmation before viewing.
Most cases involve bodies, however the site will also be used to trace living people, for example those who have lost their memory, if needed.
Joe Apps, from the Bureau, said: "The aim of the new site is to bring closure to the families and friends of the people featured.
"With new unidentified person cases we rely on modern forensic techniques for identification but on older cases we look to use every tool available and believe that case publicity is the best chance of getting images recognised.
"This will be the first time families of missing people have been able to search through records for themselves and it will empower families to play an active part in the search for their loved ones."
Members of the public will be able to search the cases and provide information online.
Any relevant details will then be passed to the police or the coroner in charge of the case.
Details of all unidentified cases, including bodies, remains and living people, will be posted on the website - apart from cases where remains are too partial to be of value.
Similar websites have been set up in certain states in the US, and by police in Belgium and Switzerland.
The Missing Persons Bureau is part of the Serious Organised Crime Agency.