Desktop, OneDrive, Box files have disappeared from MacBook -- yet the folders remain! How do I find the file contents?

Question

Recently I went to my OneDrive on my 2014 MacBook Pro to get some docs, and ALL the folders were empty.   (OneDrive is formerly SkyDrive.)  I also use BOX.  I checked the trash bins on my Mac and my OneDrive.  Nothing.  Then I realized that ALL my folders were empty -- including those on my desktop and in BOX.  ALL my work is gone.  This is a big deal...and unfortunately, I did not use Time Machine.
The whole idea of the external drive was to protect these docs.  They sync with the computer -- if the computer docs disappear, so do the contents on the external drives.  But regardless, anything that was IN A FOLDER is gone -- xls, PDFs, docs, etc.  iTunes and pics are okay.
About a week or so before this I downloaded Picasa.  Not sure if this may have had an affect on my computer.
I contacted Microsoft  and they are useless.  I went to the Genius bar, and they never heard of such a thing.  They have moved it up but haven't heard anything from Apple.  This is something that happened due to the MacBook operating system, not a virus.  I've seen other similar posts where files "just disappear" but not to this extent.
I really need some help or a forensic person to figure this out.  It is quite problematic.  I appreciate you help mucho....
THANKS!!!!

Answer 1

So this seemed to result in the outcome I wanted:
- Find the old Thunderbird profile location (.../AppData/Roaming ... THunderbird/Profiles/...default/Mail/first.account.domain/Inbox
- FInd the same location on the New laptop
Copy the first (old, backup) inbox to a new file in the New profile folder; I did Inbox.bak
Start TBird - and lo and behold, I have folders "Inbox" (recent mail since the old laptop crash) and "Inbox.bak" (the mail I thought was lost).
Looks like I need to add all accounts to the New TBird first so that it creates the profiles, and after that copy the backup Inbox & Sent files to the new profile folders.
This worked for me. Not very elegant, with several manual steps, but end result is what I needed.
It would be great if there was a smoother way for disaster recovery.
And yes, I should have had better backup policy in place. For everyone's benefit - I do Data Center systems for a living, and have seen far too many "backup" services which do not actually work in a restore situation. That's why my personal backups are direct file copies on large disks. It works, but leaves room for manual error, which is what happened here.
Actual folders, btw, I keep where I see them - "c:\users\username\Thunderbird" - for this very reason.