On Debian systems guix-daemon is provided in /usr/bin, use that one.
Also configure to use the _guixbuild group.

Index: guix/etc/init.d/guix-daemon.in
===================================================================
--- guix.orig/etc/init.d/guix-daemon.in
+++ guix/etc/init.d/guix-daemon.in
@@ -11,7 +11,7 @@
 
 set -e
 mkdir -p "/var/run"
-if [ ! -f "@localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon" ]
+if [ ! -f "/usr/bin/guix-daemon" ]
 then
   exit 5
 fi
@@ -35,8 +35,8 @@ start)
       -E GUIX_LOCPATH=@localstatedir@/guix/profiles/per-user/root/guix-profile/lib/locale \
       -E LC_ALL=en_US.utf8 \
       -p "/var/run/guix-daemon.pid" \
-      @localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon \
-      --build-users-group=guixbuild --discover=no \
+      /usr/bin/guix-daemon \
+      --build-users-group=_guixbuild --discover=no \
       --substitute-urls='@GUIX_SUBSTITUTE_URLS@'
 
   fi
