Motiqul Islam Matin filed a court case last month against the owner of the Tazreen Fashion factory after his sister was among those killed in the blaze on the outskirts of the capital.
The court ordered police to investigate the complaint against the owner and his managers, but the probe was halted last week after the officer investigating the case was transferred, police said.
Matin, 22, said he has started receiving death threats from unknown callers since lodging the case and has been forced to go into hiding.
"They also said they would find me even if I went back to my village," he said.
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Although a government probe in December last year recommended the owner face murder charges for "gross negligence", no case has been filed against him.
Matin quit his own garment factory job after the November 24 blaze to devote his time to searching for his 30-year-old sister, whose body has not been recovered from the site.
The fire at the Tazreen factory, where workers were making clothes for global suppliers, such as US giant Walmart and Dutch retailer C&A, was the country's worst industrial inferno.
The owner, Delwar Hossain, who has been barred by the high court from leaving the country, could not be contacted for comment.
Badrul Alam, police chief at the Ashulia industrial area where Tazreen is located, told AFP that Matin had not lodged any complaint about the threats.