So to summarize: For now, (as of the newest press conference), Audrii remains missing. They confirmed to have found a backpack belonging to a child that was described as wet, and that Steve is now the lone person of interest. The 2003 Chevrolet is confirmed to belong to him, and Polk County now asks for information from any resident nearby that may have seen the car within the 24 hours of Audrii being reported missing. During the conference it has now been confirmed that other items of interest have now been found too but the type and location of where and what these items are was not disclosed. Steve is now arrested on a deadly weapon assault charge that dates back to August. Unfortunately now we are past the 48 hour allotted time that is given to find a missing child and relieve them of any harm, and it's suspected now that authorities are now investigating for possible foul play.
EDIT: I'd like to also point out how the man who's been speaking at the press conferences used past tense words when referring to Audrii today, ie "She was loved by many." Unfortunately for the time being, even if the authorities already know she's gone, they can't say as to not jeopardize the integrity of the investigation.