Getting "pg_ctl: No such file or directory" when trying to start Postgres server on Mac

Question

I'm using Postgres 9.5 on Mac Sierra. My postgres db suddenly died, and so I need to restart it, but I'm getting some errors when I try and run

/usr/local/var/postgres start

below tells the saga ...

localhost:myproject davea$ sudo pg_ctl -D /usr/local/var/postgres start
Password:
pg_ctl: cannot be run as root
Please log in (using, e.g., "su") as the (unprivileged) user that will
own the server process.
localhost:myproject davea$ sudo su - postgres pg_ctl -D /usr/local/var/postgres start
-bash: pg_ctl: No such file or directory
localhost:myproject davea$ ls /usr/local/var/postgres
PG_VERSION  global   pg_commit_ts  pg_hba.conf    pg_logical    pg_notify    pg_serial     pg_stat  pg_subtrans  pg_twophase  postgresql.auto.conf
base        pg_clog  pg_dynshmem   pg_ident.conf  pg_multixact  pg_replslot  pg_snapshots  pg_stat_tmp  pg_tblspc    pg_xlog      postgresql.conf

What is the right way to start up my Postgres server on my Mac?

Edit: In response to comments, this is how I attempted to impersonate the postgres user and restart the server

localhost:myproject davea$ sudo su - postgres
Password:
localhost:~ postgres$ pg_ctl -D /usr/local/var/postgres start
pg_ctl: could not access directory "/usr/local/var/postgres": Permission denied
localhost:~ postgres$ ls -al
total 128
drwxr-xr-x+ 24 postgres  staff     816 Apr 19  2016 .
drwxr-xr-x   3 root      daemon    102 Oct 26  2016 ..
drwx------+  3 postgres  staff     102 Apr 19  2016 Desktop
drwx------+  3 postgres  staff     102 Apr 19  2016 Documents
drwx------+  3 postgres  staff     102 Apr 19  2016 Downloads
drwx------+  5 postgres  staff     170 Oct 26  2016 Library
drwx------+  3 postgres  staff     102 Apr 19  2016 Movies
drwx------+  3 postgres  staff     102 Apr 19  2016 Music
drwx------+  3 postgres  staff     102 Apr 19  2016 Pictures
drwxr-xr-x+  3 postgres  staff     102 Apr 19  2016 Sites
drwxr-xr-x  40 root      daemon   1360 Mar  4  2016 bin
drwx------  27 postgres  daemon    918 May 26 08:35 data
drwxr-xr-x   6 root      daemon    204 Mar  4  2016 doc
drwxr-xr-x  33 root      daemon   1122 Mar  4  2016 include
drwxr-xr-x   3 root      daemon    102 Mar  4  2016 installer
drwxr-xr-x  61 root      daemon   2074 Mar  4  2016 lib
-rw-rw-r--   1 root      daemon   2476 Jan 11  2016 license.txt
drwxr-xr-x   3 root      daemon    102 Mar  4  2016 pgAdmin3.app
-rwxr-xr-x   1 root      daemon    373 Mar  4  2016 pg_env.sh
drwxr-xr-x  12 root      daemon    408 Mar  4  2016 scripts
-rw-r--r--   1 root      daemon  53807 Feb  8  2016 server_3rd_party_licenses.txt
drwxr-xr-x   4 root      daemon    136 Mar  4  2016 share
drwxr-xr-x   3 root      daemon    102 Mar  4  2016 stackbuilder.app
drwxr-xr-x   3 root      daemon    102 Mar  4  2016 uninstall-postgresql.app