ADDIS ABABA, Ethiopia — Ethiopians are taking to the streets and to social media to protest their government’s failure to find at least a dozen university students and five other people who were believed to have been kidnapped from a bus by masked men in December in the latest in a chain of ethnically driven conflicts.

The students, most of whom are women who belong to the Amhara ethnic group, were studying at Dembi Dolo University in Oromia, a region populated by ethnic Oromos, officials said. The two ethnic groups, which have clashed in the past, account for about 60 percent of the population of about 100 million in this nation in the Horn of Africa.

The disappearance has stoked anger, resentment and frustration at the government, with thousands of protesters joining demonstrations in recent days to demand answers. Relatives and supporters began a campaign using the hashtags #BringBackOurGirls and #BringBackOurStudents, reminiscent of the efforts to rescue schoolgirls abducted by Boko Haram in the northern Nigerian village of Chibok in 2014.

“The families are crying — they are begging for help,” said Dessalegn Chanie, the chairman of the National Movement of Amhara, an opposition party. “These are poor farmers who have invested a lot in their kids to send them to school.”