Introduction
I'm using updated TeXlive 2014 and the fontawesome package version is 3.1.1.
The newest version of FontAwesome font is 4.2.0 and it contains icons for Linux and StackExchange.
So I downloaded the bundle from here and just replace the FontAwesome.otf in
/usr/local/texlive/2014/texmf-dist/fonts/opentype/public/fontawesome
After that I run texhash.
The code
I have a (huge) tex file with a lot of material and also the code
\def\faSkype{{\FA\symbol{"F17E}}}
\def\faSE{{\FA\symbol{"F18D}}}
\def\faLinux{{\FA\symbol{"F17C}}}
It compiles with no error and the PDF output is OK, as we can see below.

The problem
I have no idea why the MWE below does not work. The same problem without fontspec.
\documentclass{report}
\usepackage{fontawesome}
\usepackage{fontspec}
\def\faLinux{{\FA\symbol{"F17C}}}
\def\faSE{{\FA\symbol{"F18D}}}
\def\faSkype{{\FA\symbol{"F17E}}}
\begin{document}
Linux icon: \faLinux
StackExchange icon: \faSE
Skyp icon: \faSkype
\end{document}
lualatex on the code above produces (icons missing)

I found here in TeX.SE a lot of topics but that solutions didn't work for me. I'd deleted the system font installed version.

/usr/local/texlive/2014/texmf-dist/fonts/opentype/public/fontawesome. It should be in/usr/local/texlive/texmf-local/fonts/opentype/public/fontawesome. – cfr Jan 14 '15 at 02:04~/.texlive2014? – cfr Jan 14 '15 at 02:07texhash?updmap-sys? – Sigur Jan 14 '15 at 02:09lualatexagain and no success. – Sigur Jan 14 '15 at 02:14.ttfversion as a system font. That's what I've got (and it is 4.2.0) and your MWE compiles fine with bothlualatexandxelatex. – cfr Jan 14 '15 at 02:36otforttf? – Sigur Jan 14 '15 at 12:19/usr/share/fonts/TTF/fontawesome-webfont.ttfseems to do the trick. In my case, it is installed as part ofttf-font-awesomewith my distro's package manager. – cfr Jan 14 '15 at 13:16kpsewhere FontAwesome.otf? This will tell you which font the TeX engine is going to load, and you might discover that some folder with another version of the font takes precedence over the one you installed. – Xavier Jul 11 '15 at 19:30