He used his online banking account to make four 1p transactions to Cameron's account, using the space reserved for the reference number to write him messages.
"Hi, I found your wallet in the road. Text or call!" the messages read, with Simon's phone number included.
His tweet has gone viral, with people praising the good samaritan for his ingenuity.
"This took creativity. Love seeing these acts of kindness. Thanks for sharing," one person replied.
"Great to know there are still fabulous people out there who actually care. Bravo," someone else said.
Cameron said in a subsequent tweet that he hasn't paid Simon the 4p back but has sent him a bottle of red wine to thank him.