By Brad Lendon
(CNN) -- Somebody took Jessica Heeringa from a Michigan gas station Friday night. Police seem certain of that but say they're "grasping at straws" for other evidence that might help them find the 25-year-old cashier.
Norton Shores, Michigan, Police Chief Daniel Shaw said that by Tuesday morning authorities had gotten 150 tips in the Heeringa case, but nothing conclusive.
"A lot of interesting tips that we can follow up on. Whether or not they're solid, it's hard to say because we have so little to work on with physical evidence. We're just grasping at straws. ... We're grasping for straws with whatever we can find at the scene," Shaw told CNN affiliate WOOD.
Shaw said a DNA sample was found at the gas station, but he could not tie it to Heeringa's disappearance, WOOD reported. That sample is being tested.
Heeringa was scheduled to close the Exxon station where she was working alone at 11:30 p.m. Friday. But at 11:15, police got a 911 call that the station was unmanned.
"It's very suspicious why there's nobody here," the 911 caller says in a tape police released Monday.
Based on the way the station was left, police say they believe somebody abducted Heeringa.
"Her purse and other belongings were undisturbed. In addition, the store's cash drawer was found out and no money was missing," police said in a statement.
Police are looking for the driver of a silver minivan who was seen in the store's parking area late Friday, they said.
A press release describes him as a white male, between 30 and 40, with wavy hair parted in the middle. The van could have been a Chrysler Town and Country, police said.
The Exxon station did not have security cameras, but late Monday police released video they think shows the van driving by a nearby business. The video is blurry, the van is only seen for a few seconds, and neither a driver nor license plate can be seen.
"I wish I had the technology like you see on TV where you could blow it up and I could see the driver inside. But that doesn't exist for me," Shaw told WOOD. But it is something.
"It does give us some hope that we've got some accurate information out there to work with," he told the station.
Heeringa's family and friends in the community of 22,500 near Lake Michigan were posting missing posters around the area, and a Facebook page was set up for people to offer clues or support.
"We are searching! Hang tight! The whole Country wants you home!" said a Facebook post from Monday morning.
Heeringa is described as 5-foot-1, 110 pounds with blond hair, blue eyes and wearing wire-rimmed glasses.
Heeringa's mother, Shelly Heeringa, told CNN affiliate WZZM that she thinks her daughter's abductor was a past customer who knew Jessica and the store.
"She's very helpful, that's why I think he lured her out of the gas station," the mother told the station. "He knew there wasn't security cameras."
People with information that may help find Heeringa are asked to call the Norton Shores police at 231-733-2691.