The MPs are calling on Mr Raab to make contact with his counterparts in Mexico to ensure proper attention is given to the case of Claudia Uruchurtu.
Ms Uruchurtu, a Mexican national, is the sister of Dr Elizabeth Uruchurtu, who lives in Sheffield Hallam and has dual British-Mexican citizenship. She went missing on March 26 on her way home from a rally in the Nochixtlan, a town in Oaxaca in south-western Mexico.
According to her family, the missing woman had attended a rally outside the local council, where the people of the village had gathered to protest a local resident being beaten up, allegedly by security forces linked to the municipal president.
Ms Uruchurtu left the rally but never returned home and there are reports from witnesses at the rally that she was grabbed and pushed into a car.
The family have registered her disappearance with the 'National Registry for missing and non-localised persons' and have filed a complaint with Oaxaca's Human Rights Commission.
Relatives and acquaintances have travelled to the surrounding villages to Nochixtlan to try and find her in hospitals or police stations.
In a letter to Mr Raab, MPs Olivia Blake, Paul Blomfield, Clive Betts, Louise Haigh, Miriam Cates and Gill Furniss write: “As Sheffield MPs we are deeply concerned about the whereabouts and welfare of Claudia Uruchurtu. Her family suspects human rights abuses, and have no confidence that local, state or national authorities will give the priority to the case that it requires.”
Elizabeth Uruchurtu said: "Almost two weeks ago, our family got the terrible news of my sister's disappearance. She is a loving and caring individual who works actively for citizen's groups. It is our fear that her criticisms of local government and her highlighting abuse of power by public servants, is behind her disappearance.
"We are determined, with the support of our MPs, to ensure that her case remains of public concern. Raising awareness will help us find the truth and ensure that justice is done. If tragedies like this are left unnoticed, our vital freedoms and rights will continue to be eroded.”
The family have set up a crowdfunder to help pay for legal costs and are asking people to get in touch with their MPs to raise awareness of the issue further.
Sheffield Hallam MP Olivia Blake, who coordinated the letter, said: “We are all deeply concerned about the whereabouts of Claudia. I met with the family yesterday morning and have been in touch with Amnesty International and the FCDO.
"I hope the Foreign Secretary will now step in to raise the alarm internationally and do all he can to aid the Uruchurtu family in ensuring Claudia is found.”
Ms Blake has also written a joint letter with Salford and Eccles MP, Rebecca Long-Bailey, whose constituency is home to Sara Uruchurtu, another of Claudia’s sisters.
A Foreign, Commonwealth and Development Office spokesman said: “We are concerned about the disappearance of Claudia Uruchurtu in Mexico and our staff are helping her family to access support from human rights groups in the area.”
Because Ms Uruchurtu is a sole Mexican national, the Government is unable to provide consular support. Her sisters are both UK/Mexico dual nationals who live in the UK.
More information about the case can be found here.