Hey there, @Oldilocks, I'd be more than happy to look into this for you!
Did you use the app, in order to add these files to your Dropbox account? If so, had they been synced to your account online? When was the last time that you saw them there?
If I were you, I'd also have a look into the events page. The Events page at www.dropbox.com/events gives you an overview of all activity in your account including files events (adds/edits/deletes).
Can you take a look, and let me know more? Thanks!