Up to 28,000 Syrians have disappeared over the past 19 months, with civilians snatched from the streets or forcibly abducted by government troops or security forces, human rights groups say.

Relatives had been unable to discover the fate of their loved ones. Many of those abducted were almost certainly dead, while others were alive and being held in Syrian prisons or secret detention centres where they were tortured, the groups claimed.

Since the uprising against President Bashar al-Assad began in March 2011, government forces had "disappeared" peaceful protesters on an unprecedented scale, the groups said. Some campaigners have estimated the number of those who have vanished could be as high as 80,000.

A harrowing film released on Thursday by the global campaign network Avaaz shows disturbing footage of forced disappearances. In one incident, three soldiers grab two women dressed in black abayas walking down a street. They hit them and drag them away. In another, soldiers abduct a Syrian man, yanking him by the hair past a tank.

Alice Jay, Avaaz's campaign director, said: "Syrians are being plucked off the street by Syrian security forces and paramilitaries and being 'disappeared' into torture cells. Whether it is women buying groceries or farmers going for fuel, nobody is safe.

"This is a deliberate strategy to terrorise families and communities – the panic of not knowing whether your husband or child is alive breeds such fear that it silences dissent. The fate of each and every one of these people must be investigated and the perpetrators punished."

Victims were not members of the rebel Free Syrian Army (FSA), which is fighting government forces on numerous fronts. Instead, they were civilians or peaceful protesters whom the authorities suspected of sympathising with the opposition. Some were abducted from their homes after midnight, others seized at military checkpoints. None were seen again.

Fadel Abdulghani, of the Syrian Network for Human Rights which has been monitoring the death toll in Syria since the protests began, said the group had collected 18,000 names of people who had disappeared. It had information but no names for 10,000 more cases, as the families had been too afraid to share them, it said.

Muhammad Khalil, a human rights lawyer from the city of Hasaka in north-eastern Syria, said: "While there is no precise figure, thousands of people have disappeared since March last year. The regime is doing this for two reasons: to directly get rid of the rebels and activists, and to intimidate the society so that it won't oppose the regime."

Avaaz said it had spoken to numerous friends and relatives of people who had been forcibly disappeared. It said it would hand over these cases to the UN human rights council, which investigates such abuses. Forced disappearances are a crime against humanity and can be tried in the international criminal court.

Many people talk about the uncertainty of not knowing their relatives' fate. Mais, whose husband Anas was forcibly disappeared in Talkalakh in February this year, said: "The children need a father in their lives. It has been difficult to adapt. I have had a very hard time explaining his absence. They always ask me: 'Where is Dad? Who took him?' And I don't know how to respond. I have to lie to them. I tell them he is at work, that he is OK."

Others describe how their loved ones went missing. Ahmad Ghassan Ibrahim, 26, from the village of Qala'at al-Hosn, near Homs, vanished on 27 February. His mother, Fayzeh al-Masri, said: "My son drove his car from Qala'at al-Hosn to the city of Talkalakh. It was then when we lost contact with him. He called his aunt at 10.30pm from a number other than his …We later found out that the number Ahmad called us from belongs to the military security branch in Homs. We asked almost every security branch about him, to no avail.

"A month and a half ago we called his cellphone and someone answered, saying that Ahmad was killed by a regime sniper and buried in Rastan, but we were not able to confirm this information. We have been seriously concerned for six months. We are certain that he would not have left us or his wife, who is expecting twins. We only want to know his fate."

The tactic of forced disappearances is not new. Assad's father, Hafez, carried out a bloody crackdown between 1979 and 1982 – about 7,000 of those victims are still missing. During the "dirty war" in Argentina from 1977-83, it is estimated that as many as 30,000 people disappeared under the ruling military junta. Throughout the Algerian civil war from 1992-97, it is claimed as many as 17,000 people were forcibly disappeared.