Syria’s government has been accused of profiting from a black market in which people pay huge sums to find relatives who have been detained or abducted.
Amnesty International said officials and prison staff were benefiting from bribes paid to middlemen or brokers.
One rights activist said such bribes had become “a big part of the economy”.
As many as 65,000 people have been detained since 2011 in a campaign of enforced disappearances that Amnesty considers a crime against humanity.
The human rights group says those taken are usually held in overcrowded detention cells in appalling conditions and cut off from the outside world. Many die as a result of rampant disease, torture and extrajudicial execution, it adds.
Those forcibly disappeared include peaceful opponents of President Bashar al-Assad such as demonstrators, human rights activists, journalists, doctors and humanitarian workers.
Others have been targeted because they are believed to be disloyal to the government or because their relatives are wanted by the authorities.
In one case, Rania al-Abbasi, a dentist, was arrested in 2013 along with her six children aged between two and 14 years old, a day after her husband was seized during a raid on their home.
The entire family has not been heard of since. It is believed they may have been targeted for providing humanitarian assistance to local families.
Amnesty said that the campaign of enforced disappearances had become so entrenched that people desperate to find out the whereabouts of their loved ones, or whether they were even still alive, were willing to pay bribes ranging from hundreds to tens of thousands of dollars to middlemen or brokers.
A lawyer from Damascus told Amnesty that the bribes were “a cash cow for the regime… a source of funding they have come to rely on”.
Some families have sold their property or given up their entire life savings to pay bribes to find out the fate of their relatives – sometimes in exchange for false information.
One man whose three brothers disappeared in 2012 said he had borrowed more than $150,000 (£97,500) in failed attempts to find out where they were. He is now in Turkey working to pay back his debts.
The report said family members who tried to inquire about disappeared relatives were often at risk of arrest or being forcibly disappeared themselves, which gave them little choice but to resort to using middlemen.
One man who asked the authorities about his brother’s whereabouts was detained for three months and spent several weeks in solitary confinement.
“Enforced disappearances are part of a deliberate, brutal campaign by the Syrian government,” said Philip Luther, director of Amnesty’s Middle East and North Africa programme.
“It is entirely within their power to put an end to the unspeakable suffering of scores of thousands simply by ordering security forces to stop enforced disappearances; informing families of the whereabouts or fate of their disappeared relatives; and immediately and unconditionally releasing all those imprisoned for peacefully exercising their rights.”