Christian Aid Ministries has sent out an "urgent" prayer request after its workers and their children were abducted in Haiti on Saturday.
The group, who were taken near the capital of Port-au-Prince, is made up of 16 US citizens and one Canadian citizen. It includes five children.
They were returning from a visit to an orphanage when they were ordered off their bus at gunpoint while en route to the airport to fly home.
Christian Aid Ministries said they were "seeking God's direction for a resolution" and were in touch with authorities who are "seeking ways to help".
"Join us in praying for those who are being held hostage, the kidnappers, and the families, friends, and churches of those affected. Pray for those who are seeking God's direction and making decisions regarding this matter," it said.
"As an organization, we commit this situation to God and trust Him to see us through. May the Lord Jesus be magnified and many more people come to know His love and salvation."
The group is believed to have been kidnapped by the notorious 400 Mawozo gang, which was behind the kidnapping of a nun and priest earlier this year.
It is feared that they will demand up to $1m per person for their release.
Gèdèon Jean, the executive director of the Center for Analysis and Research in Human Rights, an advocacy group in Port-au-Prince, told the New York Times there was a good chance of the group being freed.
"They're going to negotiate," he said of the kidnappers. "[The hostages] are going to be freed - that's for sure. We don't know in how many days, but they're going to negotiate."