On average, nearly one person a day has been kidnapped this year, according to the United Nations, often by the Islamist extremist group, Boko Haram.
A total of 179 people have been captured so far in 2019, many of them young women and girls.
"Whether you're a farmer or trader, no one is safe from kidnapping," said Diffa city resident Lawan Boukar.
The disappearances often occur at night in villages along the Komadougou Yobe river, the natural border between Niger and Nigeria, Agence France Presse reports.
"These kidnappings are worrying a large proportion of the population and the authorities," said Bako Mamadou, mayor of Bosso, a town which has been attacked several times since February 2015.
Mamadou said some women and girls are raped and "permanently detained" by their captors.
Ransoms are usually paid in Nigeria's naira currency, he said and can exceed one million CFA francs (1,500 euros) -- a huge amount for most in the impoverished, arid nation on the edge of the Sahara.
Diffa, which borders the birthplace of Boko Haram in northeastern Nigeria, has suffered a string of cross-border raids and population displacement.
In March at least 25 people were killed in a series of attacks in the region, according to an AFP tally, as well as nine soldiers.
The next month, in the regional capital, also called Diffa, suspected Boko Haram militants launched an attack on the central police barracks, killing officers and taking hostages before eventually blowing themselves up.
In June, a would-be suicide bomber with a submachine gun was arrested outside a church in Diffa city, while four other would-be bombers were killed elsewhere.