Last Tile Finder
You buy it once for coins (Level 50 & above) or gems (Level 30 & above) and can use it to find up to 10 missing tiles per mine. It remains active in that mine until it finds all tiles (up to 10). It refills in 24 hours for use in another mine or for 30 gems to refresh it. It won’t disappear after it’s used, but will only show when in a mine.
To utilize it, enter the mine with the missing tile(s) and it will show up just above your neighbor bar. (Picture 1)

You must have 10 tiles or less in order to activate it. Click on the magnifying glass and a line will show up for the equivalent length of 15 tile spaces. (Picture 2)

Simply follow the line and keep clicking as you go until you find your missing tile. (Picture 3)

For more than 1 tile, click the magnifying glass again after clicking on the missing tile and repeat if there’s yet another.