(EVANSDALE, Iowa) -- Police searching for missing Iowa cousins Elizabeth Collins and Lyric Cook Monday began draining the lake near where their bicycles were found.
Searchers spent two days dragging the lake near Evansdale, but came up with nothing, and as yet have no other leads as to what might have happened to the two girls.
"The focus today is to get these two girls back. That's what we want ... just these girls back," said Capt. Rick Abben, a chief deputy with the Black Hawk County Sheriff's Office
"We just don't have much to go on," he said. "There's two bikes and a purse that was found. ... There's nothing really more to tell you than the search is continuing."
Evansdale city officials told ABC News affiliate KCRG-TV it would take several days to drain the lake.
Collins, 8, and Cook, 10, were last seen around midday Friday, riding their bicycles in downtown Evansdale. Police found their bicycles on Friday and a bag they were carrying on a trail near Meyers Lake. Crews used boats to search the lake, and volunteers looked in the woods Saturday and Sunday, but didn't find any sign of the girls.
Police completed the fourth day of searching, but still have no idea what happened. About 1,000 volunteers combed a 12-square mile area over the weekend in the town of about 5,000 people.
The family of the two girls is determined to find them, even as they struggled to make it through the "fourth day nightmare," with no clue as to what may have happened.
"We just ask that they continue to keep looking, not to give up," Collins' mother Heather Collins told ABC News Monday. "We will find these girls. These girls will be found."
Heather Collins said the family has strict rules with Elizabeth about how far she is allowed to go and how often she has to check in.
"If she goes more than one block, she tells us and she calls us when she gets there and she calls us when she comes home," Collins said. "This is not like her normal thing."
Heather Collins reported the girls missing about three hours after they left to ride their bikes.
"I just had a gut feeling my daughter would not leave that long," Heather Collins said. "She knows she'd be in trouble. ... That's not like her."
Police are working with federal authorities on what to do next.
"Every hour, you know, it makes it that much worse. The first 24 hours of course are very critical. We've obviously surpassed that now by quite a bit," Abben said.
No Amber alert was issued in the case, because it does not meet the requirements, Abben said.
"Because we have no person that was seen and we have no vehicle that was described, so we can't issue an Amber alert by their guidelines," Abben said.
More than 1,000 volunteers have fanned out around the area to look for the girls. The response was so overwhelming that when hundreds of volunteers showed up Sunday, search organizers said it took several hours to bus people to assigned areas. Neighbors in this small, tight-knit community say it's the least they could do to help.
"I have two little girls at home. Just want to bring them home safe to their mommy and daddy," said volunteer Kim Einfelt. "Can't lose hope. Can't."
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