Ronson, 35, is set to DJ at the annual charity Ark dinner in front of 900 guests, including Prince William and Kate, who have paid around £10,000 for a ticket to the show in London on June 9.
But just hours before he is set to play he wrote a message on his Twitter page saying he has lost his DJ bag.
He wrote: 'Last nite, my DJ bag went MISSING from THE BELVEDERE in holland park. BIG reward for anyone who helps me get it back. i cant play without it.
'contact mark.gillespie@threesixzerogroup.com or on 02030517930. there will be a HEALTHY CA$H PRIZE for anyone who can get my bag back thanks.
'THE REWARD IS WORTH MORE THAN THE LEATHER MESSENGER BAG AND ITS CONTENTS, I GUARANTEE IT. CONTACT MARK GILLESPIE +442030517930'