Missing Photos

Using Photos 3.0. Was using to airdrop for 2 photos and then drug same 2 photos to Pictures on my iMac. When I went back to Photos, all but the 2 photos were missing. No I did not delete them. They were just gone. I tried to use Time Machine and was not successful. Maybe I am doing something wrong in Time Machine, but followed Apples instructions regarding restoring a Photos library from a Time Machine backup. They still are not there. I was not using iCloud at the time. It is my understanding that iCloud only mimics what you have on your computer, so even if I had iCloud at the my pictures would still be gone? I have since put Photos on iCloud. Pictures missing and Albums are empty. Of course I now have my pics from my iPhone. Any suggestions would be greatly appreciated! HELP!