First, we ask questions. Beagles are natural wanderers, and there are a lot of them out there, so we ask questions to try and figure out how likely the dog someone spotted is Sassafras. This involves some specifics about whether the dog they had seen had a collar on, what it's size was, coloration, and behavior. It also includes trying to get as many specifics about where the dog was (what side of the street, what direction it was heading, etc, or who it was with). Recent sightings have given specific buildings, so we also try to find a phone number for those buildings (to help weed out the crank calls, unfortunately).
If nothing rules out the sighting as Sassafras, we then decide about whether to put up flyers in the area where the dog was spotted, spend time there with business cards, etc., in order to see if we can find someone else who has seen the dog who might be able to add to our information.
We might also talk to the trackers we've been working with - they make great sounding boards because they have good instincts about whether or not a sighting is a good one.
If the information we have is specific enough, we might try a track. What happens on a track? We give the tracking dog a scent item, and if Sass has been at a spot the tracking dog can follow her scent (we hope to her!).
To steal a description from Laura:
... every dog's (and, for that matter, human's) scent is unique, so [the tracking dog] follows only one that matches sass's. of course, she can pick up tons of other scents - we've tracked in places where tons of people walk dogs - but she only tracks sass's. ... it still feels like magic when we do a track because it's just impossible for us humans. on the other hand, though, it's totally rational for dogs. it's their primary sense and, as i'm trying to learn as much as i can about them, i read something about, if you want to imagine a dog's dreams, you'd have to imagine a series of smells, not of sights or sounds. the way [the tracker] explained it was that it would be like showing a human a color and asking him/her to follow the line that's that color. there would be lots of lines in other colors, but we know what that color looks like and it wouldn't be hard to follow the red line even amid green, blue, yellow, etc. lines.