Some appear to have been carried out by armed insurgent extremist groups and criminal networks seeking ransom in cash, weapons or both. But others have no declared motive. 

Foreign journalists are particular targets, mostly Europeans who have ventured into Syria, usually without the permission of the Syrian government, to cover a conflict now well into its third year. Syrian journalists have been taken, too, as have Syrians working with foreign news organizations.

Foreign reporters were initially welcomed by many insurgents and Syrian civilians, taken for advocates who could publicize grievances against President Bashar al-Assad. Now they are sometimes viewed as interlopers who have no stake in the outcome of the conflict, which has left more than 100,000 people dead. 

Spreading economic desperation in Syria has increased the possibility of betrayal, extortion and abduction, according to news media advocacy and rights groups. Some translators, drivers and local guides have reported that criminal groups or jihadists have tried to recruit them to lure journalists into Syria with promises of scoops. 

“There have been more abductions and there have been nastier abductions,” said Donatella Rovera, a senior investigator for Amnesty International who has spent long periods traveling in Syria to document rights abuses in the conflict. “There is no denying that the fragmentation of armed groups, and the increased visibility of radical groups, have coincided with an increase in abductions,” she said. “It’s fair to assume there is a relationship there.” 

The Committee to Protect Journalists, a New York-based advocacy group, has reported at least 14 cases of local and international journalists who are missing or have been abducted this year. 

Reporters Without Borders, based in Paris, has recorded 15 cases of foreign journalists who are missing or have been abducted or arrested. But the total number of abductions is believed to be significantly higher because many cases have not been publicly disclosed, usually at the request of the victims’ families, partly for fear of angering the kidnappers or emboldening them to demand higher ransom payments. 

Even at the reported numbers, the pace of abductions of foreign journalists appears on a trajectory to surpass the 25 cases in Iraq in 2007, at the height of the conflict there. 

“We see more journalists not abducted by the government, but by independent militias who are going after money, and this is worrying,” said Sherif Mansour, the Middle East and North Africa program coordinator for the Committee to Protect Journalists. The trend toward cash ransom, he said, started in late 2012, “but we can see from the targeting that basically they’re going after nationalities that are going to pay.” 

Jonathan Alpeyrie, a French-American photojournalist for the Polaris agency, was abducted by Islamist fighters near Damascus on April 29 and released nearly three months later. He said a $450,000 ransom had been paid on his behalf. 

“The rebels are so desperate they don’t care about their reputation abroad,” he said in an interview published on Wednesday by the Paris-based Journal de la Photographie. “They see guys like us as an opportunity.” 

Ricardo Garcia Vilanova, a photojournalist and cameraman who has spent more than 13 months in Syria over multiple trips since the conflict began in 2011, said he had sensed a new mistrust toward the foreign news media on his most recent visit. He said many Syrians who opposed Mr. Assad resented the Western military reluctance to intervene. 

The list of cases in the past few months includes both Syrian and foreign journalists. On July 25, three Syrian employees of Orient TV, an opposition television channel, were abducted in the northern town of Tel Rifaat: Obeida Batal, Hosam Nizam al-Dine and Aboud al-Atik. On July 24, a Polish photojournalist, Marcin Suder, was taken in the northwestern province of Idlib. On June 6, two French journalists employed by the Europe 1 radio station, Didier François and Edouard Elias, disappeared near Aleppo. On April 24, a Belgian academic, Pierre Piccinin de Prata, who was reporting for the Brussels newspaper Le Soir, disappeared. On April 9, Domenico Quirico, an Italian journalist for the newspaper La Stampa, went missing near the western city of Homs. 

Two Americans journalists were publicly acknowledged to be missing in the past year. Austin Tice, a freelancer who had written for The Washington Post, McClatchy newspapers and Al Jazeera’s English-language channel, disappeared near Damascus almost one year ago. And James Foley, who had worked for GlobalPost, a Boston-based news Web site, disappeared Thanksgiving Day in Idlib.

In Mr. Foley’s case, an initial decision was made to withhold news of his disappearance, said Phil Balboni, the chief executive and co-founder of GlobalPost, while it quietly investigated what might have happened. Six weeks later, after consultations with Mr. Foley’s family, GlobalPost announced in a news article that he had been kidnapped by unidentified gunmen. 

“We reached the point where we concluded that his likely abductors weren’t going to harm him in any way if we went public,” Mr. Balboni said. Based on information from what he described as credible sources, Mr. Balboni said he believed Mr. Foley had been abducted by pro-Assad militiamen and later turned over to the government in Damascus, despite official Syrian denials. 

Peter N. Bouckaert, the emergencies director at Human Rights Watch, said overall abductions began to increase when fighting broke out last year in Aleppo, the country’s once-flourishing commercial hub. 

The abductions have increased as the insurgency’s reliance on jihadist groups, like the Nusra Front and the Islamic State of Iraq and Syria, has grown. “They try to kidnap wealthy Syrians and some journalists for ransom,” Mr. Bouckaert said in an interview in June with Syria Deeply, an independent blog about the conflict. “The kidnappers tend to know the wealth of their victims,” he said. 

Mr. Bouckaert said a second category of abduction, in which Sunnis and Shias kidnap each other in tit-for-tat hostilities, has also increased. Unexplained disappearances have proliferated as well, he said, “where people are taken by unknown gunmen and never seen again,” as in the case of two archbishops from Aleppo who vanished in April. 

“In general, instability is on the rise in Syria, and these kidnappings are part of this instability,” he said. “Kidnappings are a part of the dangers that civilians in general face in this conflict.”