The reward would also cover information leading to the arrest and prosecution of anyone responsible for the disappearance of fifth grader Celina Cass, Supervisory Special Agent Kieran Ramsey said at a news conference at the Stewartstown Community School.
"This reward should not be read into that we are transitioning in any way in this investigation," Ramsey said, adding that recent, successful cases of recovered missing children have resulted in vigilance from the public.
"We are still aggressively - aggressively - searching and hoping to bring Celina Cass home," he said.
Jane Young of the state attorney general's office said a community member was adding a $5,000 reward for any information leading to the discovery of Celina.
Celina was last seen Monday night at her home computer near Stewartstown, which is about a mile from the Canadian border. Numerous investigators have knocked on over 300 doors in the area and in neighboring Vermont and have searched fields, woods, ponds and a river.
"We have at least another 100 men available to come in and assist with this investigation when needed," Young said.
Young said later Saturday that dive teams would be brought in on Sunday, but she would not specify where they would search for the girl.
Police have said there is no indication Celina ran away or that someone took her. She lives in a three-story house with her mother and stepfather.
Lt. Robert Quinn of the New Hampshire State Police said he's been in contact with the heads of the state police in Massachusetts, Vermont and Connecticut. "They've shown an overwhelming support for us in this investigation," he said. "They will be sending additional resources here today."
He added: "We're going to do whatever it takes to locate this lost child."
Fliers featuring photos of the girl with a gap-toothed smile were put up throughout Stewartstown and neighboring communities. Residents have passed out purple and pink ribbons and held vigils.
Celina is 5 feet 5 inches tall, weighs about 95 pounds and has hazel eyes and waist-length brown hair.