The first proof is the video of he being kidnapped is uploaded with custom thumbnail. If he really kidnapped and the kidnapper uploaded the video, the kidnapper 99% won't care about custom thumbnail.
The second proof is, his girlfriend "CutiepieMarzia" is okay and go to the cinema today. How? Yeah, because that all drama. Marzia ruined the drama. How can you go to the cinema when your boyfriend is kidnapped? Marzia went to the cinema 7 hours after pewdiepie "Kidnapped". She even posted on her instagram:
The third proof, or we can call this "a reason" of this drama, is Pewdiepie just hit 45 million subscribers. The "pewdiepie got kidnapped" might be just a drama to celebrate his achievement.
So, you still believe that Pewdiepie got kidnapped? Well, I say thats fake.