The friends of Muhammad Wisam Sankari told a Turkish gay rights group, kaosgl.org, that they had been threatened by violent male gangs.
"I am so scared," one of them said.
Mr Sankari, a refugee, arrived in Istanbul a year ago. His body was found in Yenikapi, a central district, on 25 July. No arrests have been made.
Kaosgl.org reported that Mr Sankari had been trying to get to another country as a refugee because his life was in danger.
One of his housemates, called Rayan, said a male group had kidnapped Mr Sankari about five months ago, beaten him up and raped him.
"We complained to the police headquarters but nothing happened," he said.
Another of Mr Sankari's friends, Diya, said the United Nations was also failing to protect the gay community in Turkey.
"I get threats over the phone... It does not matter if you are Syrian or Turkish, if you are gay you are everyone's target. They want sex from you and when you don't they just tag along... Who is next?" Diya said.
In June, Turkish police fired rubber bullets and tear gas to disperse gay activists who tried to hold an LGBT rally in Istanbul, despite a ban on the Gay Pride parade.
Unlike in many Arab countries, homosexuality is not illegal in Turkey but analysts say homophobia remains widespread.
Cagil Kasapoglu of the BBC Turkish Service says hate crimes against LGBT individuals in Turkey mostly go unreported.
According to kaosgl, there has been a rise in human rights violations based on sexual orientation in recent years.
Under the heading "hate crimes" the organisation recorded five murders, 32 attacks and three suicides in Turkey last year.
It believes the number of such murders over the past six years is more than 50.
Syrian gay refugees in Turkey suffer even more, as their legal status is precarious - they are usually undocumented and most are reluctant to report assaults to police, our reporter says.
The Turkish authorities cited "safeguarding security and public order" as the reason for banning Gay Pride in Istanbul this year. The parade was also banned last year.
Assaults on LGBT people in Turkey have mostly been blamed on ultra-conservative Muslims and an ultra-nationalist youth group, the Alperen Hearths.
The harassment is also related to a rise in homophobic rhetoric in conservative media and social media, Cagil Kasapoglu says.
Such rhetoric was used by Turkish ultra-conservative media when reporting the murder of 49 people in June by a gunman in a gay nightclub in Orlando, Florida, she says.
Gunman Omar Mateen, a US citizen, appeared to have an interest in Islamist extremism.

6 June 2016 Last updated at 12:49 BST
The loophole could mean thieves who exploit the bugs gain time to break into and steal a vehicle.
The vulnerability can also be used to fiddle with some of the car's settings and drain its battery.
The wi-fi weaknesses have been demonstrated to Mitsubishi, which is now working on a way to fix them.
Read the full story

The 28 prefabricated homes will provide emergency housing for people who would otherwise be forced to stay in bed and breakfast accommodation.
Reading Borough Council said it had about 120 families staying in guest houses at the end of 2016.
Work begins in Lowfield Road on Tuesday with the first residents due to arrive in the autumn.
The development, on the site of a former mobile home park, will consist of seven timber-clad blocks of four units, two storeys high, a children's play area, car parking and bike sheds.
Each unit will have two bedrooms, a bathroom, kitchen-diner and a living room.
The 28 homes are intended to house homeless families while they are waiting for authority-owned or housing association accommodation to become available.
Legally councils can house families in temporary accommodation for a maximum of six weeks.
The council said the stock of affordable housing in Reading had reduced because of high land prices and rents, as well as right-to-buy sales.
Housing councillor Richard Davies said: "Reading, along with many other towns and cities in the region, has seen an increase in the number of families requiring emergency housing.
"This has resulted in the council being forced to use bed and breakfast accommodation which is unsuitable and disruptive for homeless families."
The headless, mutilated body of a gay Syrian man has been identified by gay housemates in Istanbul who say he had been gang-raped previously.
[NEXT_CONCEPT]
The alarm on Mitsubishi's Outlander hybrid car can be turned off via security bugs in its on-board wi-fi, researchers have found.
[NEXT_CONCEPT]
Work is to begin on a temporary housing scheme for homeless families in Reading.