Demeter 0.9.24 does work for me on El Capitan (10.11.5). In fact, I did a
sudo port upgrade outdated

and many packages updated, and and Demeter still lauches and seems to run.

Yuan, you say you upgraded to 10.11. Does that mean you had Macports / Demeter working on 10.10 and it failed to work when you upgraded? If so, you might try completely uninstalling Macports and starting over.

Just for fun (well, maybe chasing Pokemon or over-analyzing Brexit is more your thing, but this works for me), I just moved my "/opt" and "/Applications/Macports" folder, reinstalled the Macports package, and then re-installed with

sudo port install demeter

(I think you don't need to specify xorg-server) and it magically worked.

So, maybe try uninstalling and installing again? Or maybe try installing without xorg-server?

--Matt