Your photos were never in Lightroom; Lightroom only displays thumbnails (called previews) of your photos. Thus, at best you can only recover the previews, which will be smaller sized and lower quality than the original photos. In order for that to work, you need to find a catalog file that displays the previews (the catalog with 0 pictures in it won't help). Look under File->Open Recent and see if you can find a catalog file which displays these previews. If you find such a catalog file, you can recover the previews via a plug-in
In general, to recover lost photos you should:
1. Restore from the Trash/Recycle Bin if they are in there
2. Restore from backups of your photos
3. If you don't have backups of your photos ... why not? ... you need to begin making regular and automated backups of your photos AND catalog file to a different hard disk, no excuses ...
4. Try an "undelete utility" which may be able to recover deleted files ... there are free ones available ... if you get down to this step, do not perform any other tasks on your computer except find and use this program
5. If that doesn't work, recover previews from Lightroom