By Agence France-Presse
Rights groups say 30 human rights activists have disappeared or been murdered in Thailand since 2001.
While local officials have been accused of being involved in some cases, they are rarely held accountable in a country where the police and courts are warped by power and influence.
A draft law on preventing enforced disappearances is currently in parliament.
But the bill must be toughened up as it currently is focused "on protecting government officials", said Angkhana Neelapaijit of Thailand's National Human Rights Commission.
"The state must stand with the victims."
Angkhana is the wife of prominent Muslim human rights lawyer Somchai, who disappeared on this day 15 years ago when he was bundled into a car off the streets of Bangkok, according to eyewitnesses.
Well-known for representing clients accused of insurgency-related violence in Thailand's deep south, Somchai's abduction came while he was defending suspected Islamic militants who had accused authorities of torturing them while in custody.
Five police officers -- one of whom was briefly jailed -- were eventually acquitted in Thailand's Supreme Court, a verdict that is a stain on the country's law enforcement record.
"Bringing perpetrators to justice... cannot be ignored, no matter the level of the government official," Angkhana said during a memorial event at the Netherlands Embassy in Bangkok.
"The families of the disappeared -- including myself -- are still waiting for justice."
The event Tuesday was attended by family members of other disappeared activists around the region, including Shui-Meng Ng, whose husband environmental campaigner Sombath Somphone went missing in 2012 in Laos.
Speaking to a sombre crowd, Shui-Meng urged the Thai government to give closure to Somchai's family, saying she "stands in unity with your pain... with your anger and indignity".
Somchai's unsolved case is one of at least 82 cases of enforced disappearances in Thailand since 1980 recorded by the United Nations.