The Malawi authorities have told gay activists who put up posters and distribute leaflets on the streets anonymously to "come out in the open".
Government official Kingsley Namakhwa said it was against the law to mount such campaigns anonymously.
But he also pointed out that homosexuality was illegal, and anyone promoting it would be prosecuted.
Rights groups have recently criticised Malawi for prosecuting two men who got engaged to each other.
Tiwonge Chimbalanga and Steven Monjeza, believed to be the first gay couple in Malawi to start the marriage process, have pleaded not guilty to charges of public indecency.
Their trial is due to start soon.
"As far as the Malawi government is concerned we only have two gays in Malawi - Steven Monjeza and Tiwonge Chimbalanga," said Mr Namakhwa.
"If there are others, let them come out in the open."
The BBC's Raphael Tenthani, in the main city Blantyre, says the police have intensified the hunt for a man who they believe is behind a gay-rights campaign.
It follows the conviction of a 21-year-old man for pasting gay-rights posters on poles along the streets.
Peter Sawali had put up posters saying "gay rights are human rights" and was convicted of conduct likely to cause a breach of the peace.
Police say Sawali had been given the posters by another man - whom they are now trying to track down.
Sawali was sentenced to community service for his crime - our correspondent says his punishment is to clean the premises of Blantyre Magistrates Court for 60 days.