torsocks not working in El Capitan
The problem doesn't appear to be in "tor" or "torsocks". The problem seems to be in the version of "curl" shipped with El Capitan.

Similar to yourself if I try torsocks curl -s https://check.torproject.org | grep Congratulations I get nothing back.

However if I try torsocks wget -qO- https://check.torproject.org | grep Congratulations I get the expected replies.

  Congratulations. This browser is configured to use Tor.
  Congratulations. This browser is configured to use Tor.


But if you install curl from brew (resulting in a newer version of curl than ships with El Capitan) and then run torsocks /usr/local/Cellar/curl/7.45.0/bin/curl -s https://check.torproject.org | grep Congratulations, you get the expected "Congratulations" messages (note the version number might be different by the time you try this).

  Congratulations. This browser is configured to use Tor.
  Congratulations. This browser is configured to use Tor.