Pof is difficult to maintain, especially on Linux, since it dynamically links to many different libs; each distribution comes with a different revision number for each lib.
So it's virtually impossible to compile Pof in a way that it's compatible for every distribution.
My current workaround is to include most of the libs in Pof distribution, in the pof/libs directory.
Unfortunately FLAC is not included in those included libs, so Pof tries to link with system libraries, but there's no more libFLAC.so.8 in your system version.
You can try to copy this lib from an older Linux distribution, try the one attached here (it's actually a renamed libFLAC.so.8.3.0). But it's possible other missing libs will appear then...
The real solution would be to compile Pof for each distribution. But other problems arise there : openFrameworks is not yet ready for that. In particular, all dependency libs must be recompiled with the -fPIC flag, to allow building a dynamic library. I do it manually each time I want to update OF... and it's a PITA. I still have to ask OF to add fPIC to every lib compilation flag.
I really hope I can find the availability to continue maintaining Pof in the future.