The family of Wanchalearm Satsaksit on Sunday called on the government and international agencies to help find the activist, who went missing after he was allegedly abducted in Phnom Penh, Cambodia last Thursday.
Sitanan Satsaksit, the missing anti-government activist's sister, made the plea on behalf of their family.
Mr Wanchalearm, she said, was a victim of forced disappearance, as he was abducted in broad daylight just outside of his Phnom Penh apartment last week. "It has been more than 65 hours since he disappeared, and his fate remains unknown," she said.
"We don't have any grudges against those who committed this crime. We pray that they will free [Mr Wanchalearm] soon. We are looking forward to his release, and we hope that this abduction will be the last case of forced disappearance," Ms Sitanan said.
She urged state agencies and international organisations to help investigate Mr Wanchalearm's disappearance, calling the incident a "gross violation of human rights" which leaves society in fear and in despair.
Mr Wanchalearm had been living in a self-imposed exile for more than six years, after his firm stance against the 2014 coup and resulting military rule led to harassment and other forms of threats to his life, she said.
Rangsiman Rome, a Move Forward Party MP who is also spokesman of the House committee on legal affairs, justice and human rights, said he will ask the committee on Wednesday to consider summoning state agencies to give information on Mr Wanchalearm's disappearance.
It will include the national police chief, commander of the Royal Thai Police's Special Branch, director-general of the Department of Consular Affairs (DCA), and head of the Protection of Thai Nationals Abroad Division under the DCA, Mr Rangsiman said.
According to a report by anti-authoritarian media outlet Prachatai, Mr Wanchalearm -- a known critic of the government -- was dragged into a black car last Thursday by a group of armed men as he went out to buy food near his apartment.
An AFP report said Cambodian authorities ruled out an investigation because it has yet to receive a report of the disappearance.
A native of Ubon Ratchathani, Mr Wanchalearm was wanted by authorities for defying a National Council for Peace and Order summons to report after the 2014 coup. As he failed to show up, a warrant was issued by the military court for his arrest.
In June 2018, police issued another warrant for his arrest, saying Mr Wanchalearm violated the Computer Crime Act by operating a Facebook page critical of the government.