It seems that you do everything the correct way, tokenized and searchable are the right settings and indeed you need to save the data pipe-separated.
I tried it in my example site and :
mysite.com/Search?searchtext=+Author:5 gives the correct results.
So this value
+authors:77 in the querystring searchtext should return results. So my guess is that or the field is not indexed or not stored correctly.
You can open de index inside an tool called Luke than you can check if the field is really inside the index. If not then you can try saving again the document, check in de DB if the field is stored (pipe-separated), rebuild the smart search index, clear the cache to be sure and then try it again.
If this answer helped you, please vote for my answer :-)