Hundreds of people in Sri Lanka's north who responded to a police announcement about relatives held in detention say they have been given no information.
Ten days ago police said they would give details about those detained in the war, which ended in May 2009.
BBC Sinhala has learned of only one man out of hundreds who went to the former war zone of Vavuniya and actually found out where his relative was.
Thousands of families are still seeking loved ones two years after the war.
Almost all of them are Tamils, living in the former war zone in desperation because of their missing husbands, sons or daughters, correspondents say. Some have been missing for many years.
Police say information will only be made available to "close relatives".
Police spokesperson Prishantha Jayakody said three centres - in the north, south and in the capital, Colombo - which would provide details of people held by the police Terrorist Investigation Division (TID).
Many saw their loved ones forcibly conscripted by Tamil Tiger militants. Of these, correspondents say, many were thought to have come out of the war alive but were detained by the government and have not been seen since.
In Vavuniya, part of the former war zone, thousands went to find out the fate of their loved ones, our correspondent says. Because of the large numbers of people turning up, only 200 people a day were able to make inquiries.
"My 26-year-old son Pradeep was taken by the Criminal Investigation Department when he went to Colombo to get his passport. That's all we know," Mylu Shanmugathas from Tellipalai told BBC Sinhala's Dinasena Ratugamage in Vavuniya.
He has been missing since 2008. Mr Shanmugathas has been to police stations, military camps and human rights offices in search of his son.
The man who was told where his son was immediately boarded the first train out of town to the southern city of Galle, where his son was being held, our correspondent says.
Others said they were looking for the sole breadwinner in their family.
"There is no one to provide for me. Who will look after me or care if I fall ill?" said one Tamil woman whose son had gone missing since being taken by police in 2007.
TID officials in Vavuniya say that they are unable to provide details of the "disappeared".
Meanwhile in another northern town, Kilinochchi, people have tried to organise a demonstration asking where their missing relatives are.
The organisers told the BBC that the army obstructed the event, sending away more than half of the 150 parents who tried to attend before letting a smaller protest take place.
It was not immediately possible to reach the Sri Lankan military spokesman for comment.
The Committee for the Investigation of Disappearances Sri Lanka says that it has recorded details of more than 5,000 disappearances since 2006.
Minister Mahinda Samarasinghe says about the same number of people are being held in "rehabilitation centres" on suspicion of being former Tamil Tigers.