How to recover photos

Registration date
Thursday August 20, 2015
Last seen
August 20, 2015
Hello. I have a bit unusual query. Actually i am using gallery lock lite app. I locked photos and videos a month back. I checked app 2 days ago and all the files were visible but last night when i opened app, it is actually showing the number of files locked i.e 272 but when i open locked folder in gallery lock app then it is showing only blank 272 thumbnails and when i open a thumbnail then it comes blank. I am not very much worried that where my files gone. I also checked my files in my Samsung galaxy s4 phone. There is no data directory folder showing neither in sd card nor in internal memory. I remember, there used to a folder in my files names gallery lock. But i haven't deleted it or it could be deleted by mistake. I also tried backup/restore option in gallerylock app but nothing happened. So please please please tell me how can i restore my photos and videos and why app showing that blank thumbnails. Please resolve my query . I will be very thankful to you all.
thanking you