The Superbad comedian reportedly entertained 20-year-old Keough at club Boujis last month. Subsequent pictures of the two leaving hand-in-hand have since prompted speculation that they are romantically linked.
A source told Star: "Jonah and Riley partied side by side all night. She had her hand on his leg and was whispering in his ear... [She was] laughing at every word he said."
As previously reported, Hill recently signed up to produce and star in forthcoming rom-com The Best Thing About Pam Rooney.