The gig will take place tomorrow night at London's 93 Feet East and will feature YouTube musicians Ed Plant and Tom Milsom as well as Chartjackers vocalists Adam and Miranda.
Johnny said: "We have a very special guest who's coming to play, and this special guest is actually a singer-songwriter who we interviewed at the very start of the Chartjackers project.
"Some of you might already know who I'm talking about if you followed this from the start, but if you don't, then let me reveal for you now that our special guest is Chesney Hawkes. Chesney Hawkes is going to be coming along and playing some songs from us."
Adam and Miranda will perform the single 'I've Got Nothing', which Hawkes has predicted could achieve its goal of topping the charts.
Tickets for tomorrow's show are £3.50 to cover costs. Any profits raised will be donated to Children In Need.
'I've Got Nothing' is released on November 9.