Nigeria has the highest number of registered missing people because of conflict in the world, the International Committee of the Red Cross (ICRC) says.
There are nearly 22,000 people registered as missing with the charity.
A spokesperson for the organisation has told the BBC the true number is likely to be much higher.
Most of them are children separated from their families during the decade-long insurgency of the Islamist group Boko Haram.
Families often get separated in attacks by the militants or are held by authorities in detention.
Many parts of north-eastern Nigeria remain inaccessible because of ongoing insecurity.
Other factors like the geographical spread of the affected area, as well as limited mobile phone capability, make the reunification process particularly tricky.
Only 367 missing people have been found in Nigeria to date since the start the ICRC began tracing those missing in 2013.
For Peter Maurer, ICRC president, access is crucial to reuniting families.
“In Nigeria there is broad territory, and groups which are out of reach of ICRC, and so population under control of these groups are not reachable by the ICRC and that’s the reason why it’s more difficult to get the data together to reunify families as in other places,” he said.