"So far all the leads have lead to dead ends," Milwaukee Police Department spokesperson Anne E. Schwartz told reporters.
Officers have been searching vacant houses, vacant vehicles and the homes of registered sex offenders in the area where the boys were last seen, but there has been no sign of them, said Schwartz.
Police also haven't found any evidence of a crime, but the lack of tips has been unusual.
"We haven't gotten calls from people who've said, 'I've seen them here or there,'" Schwartz said.
Officers have been to three-quarters of the homes in the area, Schwartz said.
Family members have issued a plea for the return of the two boys, 12-year-old Quadrevion Henning and 11-year-old Purvis Virginia Parker. Relatives and police say the two are well-mannered boys who would never run away on their own.
Family and friends held a news conference late Tuesday afternoon urging that anyone holding the children or with any knowledge of what happened to them contact authorities so they can come home.
"Whoever has them please send them home, let them go because these are good boys; they've not done anything wrong," said family friend Sonja Carroll. "They are the type of boys that don't run away, they don't run from anything they don't need anything, they just need to come home."
Relatives described the boys as good students who would never leave without permission.
"It isn't in his character to do that," said Angela Virginia, Purvis' mother.
"Sometimes you can make mistakes, but it's never too late to correct those mistakes," said Quadrevion's father, Quentin Henning, who returned from Texas after his son's disappearance. He made an appeal to anyone who might have abducted the boys: "Have a heart, have the decency to bring them back home."
The department frequently gets reports of missing children, but they typically have a history of running away and turn up quickly, Schwartz said said. The two boys do not have a history of running away.
"This is a very long time for these children to be missing," Schwartz said.
A Florida group called A Child Is Missing was helping police in the search. The group called all home and business telephone numbers within a mile of where the boys were last seen and played a recorded message about the pair, Schwartz said.
Police also contacted all registered sex offenders in the area and searched their homes, which turned up nothing, Schwartz said.
"We have tremendous resources expended to look for these boys," Schwartz said. "There is virtually no stone we have left unturned to find these boys."
The boys were last seen playing outside a home around 3:30 p.m. Sunday. One of their grandfathers told them to come inside, but they asked to keep playing and the grandfather let them, Schwartz said.
The grandfather called police at 8:30 p.m. Sunday.
"It's been very hard for the kids and it's been very hard for the staff, too," said Debbie Alt, Purvis' teacher at Elm Creative Arts School. "We're trying to go on, but it's very difficult with that empty seat."