This may have already been said, but if we were to consider the dots on the Finding Mollie website as the movements of TWO people the map seems to make perfect sense. Mollie would be the dot at 385th, and a trucker or patron would be the dot at the TA truck stop. Those dots converge at or near the car wash downtown. The other two dots perhaps represent an "escape route", the last of which being where the Fitbit apparently registered last.
So, if this is the case, they may have a trucker in mind, or someone they know was at that truck stop and also seen on camera along the route they have laid out. They may be looking for corroborating eyewitnesses that actually saw an encounter, or just before or after it.
https://findingmollie.iowa.gov/
JMO.