The striker has penned a three-year contract at the KC Stadium and will join up with the Tigers' development squad for their pre-season in July.
"He's one for the future. He's still just a kid who hasn't really developed yet," Steve Bruce told the Hull Daily Mail.
"He's scoring goals in a man's league, which is always a good sign, and we'll look to see if he can keep improving with us. Any kid who's going up against men and scoring goals has got something about them.
"The next step is to see how he goes training full-time next season."
Folkestone play in the Isthmian League Division One South.