I recently imported images from several cards into LR 5 and had them imported into folders by date and each time I imported I saw the images. When we recently connected the drive I saw the dated folders but there were no images in those folders. Are they lost forever or are they hidden somewhere? When looking on the drive through the finder it shows the folders are empty...
Please try and search those images in Lightroom under all Photographs section.
The images must have copied to the different folder but it should there in Lightroom.