Asus Zenfone hardware was ready to support OTG but the software does not. Recently Asus Zenfones received an OTA update which enabled the OTG support on it.
This update also provided
Skin brightening feature to beautification mode
Additional 3Mp and 2MP resolutions for camera
Support Asus unlock APP
Enhanced third part application compatibility
Improved Modem for better stability
There is another happy news for the Zenfone users, Asus confirmed that KitKat for Zenfone is in the final stage and also the Android L is on the roadmap. The comment on the play store says
Kitkat support on Zenfone is still under construction, it's in the final testing stage. I believe it'll be coming very soon, please stay tuned. Of course, android L is also on our road map! Remember always keeping an eye on our web site for the further news about L. :)
You can check the comment and reply here.