Does Serif Photo Plus exist for Mac?
I have searched on Google, but only found some Serif Photo Plus software working on Windows.
No, the software was not developed to run on Mac OS X. According to the official website, you can install the application only on Windows systems. However, it's possible to install it in two ways:
Install Windows through Bootcamp or Parallel Desktop. This process is called virtualization. Personally, I would recommend using Parallel because it runs Windows while Mac is also running. Mid to high processing power is recommended.
Install WineBottler and then run PhotoPlus through the program. Wine allows you to run Windows apps inside Mac without a proper Windows installation.