Do hope he gets it back.
Check ebay SEVERAL TIMES A DAY, something put on "buy it now" can go within minutes.
Also check "completed listings" daily.
To do this type   "banjo" into "buy", click search, (all banjos for sale will come up) go to yellow sector on left side of page, scroll down, tick box "completed listings" scroll down, click search.
This will bring up all the banjo sales for the last few weeks, click on any that might be the stolen one, scroll down as the picky will be at the bottom of the page.
If he has to buy a new one, tell him to tke it down the vets & get it chipped!
Good luck.
Skipy