The announcement by the regional governor of Tanzania's largest city, Dar es Salaam, has also led to a new US State Department travel warning calling on US citizens to remove any social media material found in Tanzania. Homosexuality laws could "hurt".
"I have closed my office today and we will not have time to operate," said James Wandera Ouma, one of the few activists open to LGBT rights in the country.
Another well-known activist, who can not be cited for security reasons, said gay Tanzanians have gone underground.
"We are worried about those who are known to the community as well as those who are closed," he said.
The LGBT community in Tanzania has previously suffered from popular and police ill-treatment, but last week the regional governor of Dar es Salaam vowed to set up a working group to rally and arrest people suspected of being gay.
"I announce this to every citizen of Dar es Salaam – if you know gays, let me know," Paul Makonda said in a press conference with local reporters on Monday.
The task force should be started this Monday. So far it is unclear whether the governor's deadline is met.
Several attempts by CNN to reach Makonda were unsuccessful.
"It is deeply regrettable that Tanzania has made such a dangerous decision to deal with an already marginalized group," said Joan Nyanyuki, Regional Director of Amnesty International for East Africa, the Horn and the Great Lakes.
"The idea of this task force must be given up immediately, as it only leads to hatred among the citizens."
Central government not on board
On Sunday, the Tanzanian government tried to distance itself after intense international pressure from the plans of the controversial governor.
"His views are not the government's view, and the state would like to take this opportunity to reassure people that they will continue to respect all organizations that are human rights related," a Foreign Ministry statement said.
The statement neither criticized the actions of the governor nor reassured gay Tanzanians of protection.
"If the government really means, then they should stop these actions of Makonda, otherwise the harassment and the fear will just go on," said the LGBT activist.
Ouma said until people get protection guarantees, people just stay hidden.
"I need the government's assurance that I'm not attacked," he said.
Tanzania is a deeply conservative country and unlike neighboring Kenya has not seen any progress in LGBT rights.
On the contrary, under the current administration of John Magufuli, rights groups believe the situation has worsened.
Human Rights Watch says the government has shut down LGBT-friendly clinics, banned community organizations from taking HIV control measures against the population, and detained activists who hold legal counseling workshops.
LGBT people in Tanzania are sentenced to 30 years in prison for gay male sex. This is a remnant of colonial laws. It reflects severe penalties for same-sex relationships in many African countries.
But the prospect of a research group researching "evidence" for LGBT Tanzanians on the streets and on social media has terrified many in the community, which already has a homophobic community and government.
But the activists contacted by CNN say they refuse to leave.
"I have to help people who are hiding, the government must stop this harassment, we are all citizens of Tanzania," said the LGBT activist.