Best, 34, has not been seen in more than a week and the FBI is involved in the investigation.
Best was last seen Friday, April 15 after she dropped off her 15-year-old daughter at a friend's home at the Rosewood Apartments in Round Lake Park. Surveillance cameras show her minivan coming and going. That, police say, was the last sign of her.
Investigators say they did not have many leads because Best does not have a cell phone or credit cards. They say they hope the FBI can help.
"There is no indication at this point that there is a violation of federal law that would give us jurisdiction to unilaterally investigate her disappearance, but as we do when we're asked for help by local departments and we have the resources to provide assistance, we do" said the FBI's Ross Rice.
Husband Clint Best posted a message on Facebook Monday night thanking everyone for their prayers and help in finding the missing mother.
"She would always call me and tell me where she was," he said. "She was, you know, pretty responsible about thinks like that. It's completely unlike her to just disappear this."
Best was last seen in a green 1993 Pontiac minivan and wearing a sweatshirt with the word "Chicago" on the front.
A news conference organized by police is set for 11 a.m.
