After installed plugin"serverless-plugin-existing-s3", still missing

After installed plugin, still missing. Looks like the sls doesn’t recognize below plugin.
That’s the deploy error:
Serverless plugin “serverless-plugin-existing-s3” not found. Make sure it’s installed and listed in the “plugins” section of your serverless config file.
I install command.
sudo npm install -g serverless
sudo npm install -g serverless-plugin-lambda-dead-letter
sudo npm install -g serverless-plugin-existing-s3
sls version:
Your Environment Information -----------------------------
OS: darwin
Node Version: 11.10.1
Serverless Version: 1.38.0

I can find the sls and two plugin in below location
drwxr-xr-x 24 root wheel 768 Feb 28 14:09 npm/
drwxr-xr-x 11 root wheel 352 Mar 4 13:54 serverless/
drwxr-xr-x 10 root wheel 320 Mar 4 13:55 serverless-plugin-existing-s3/
drwxr-xr-x 8 root wheel 256 Mar 4 13:55 serverless-plugin-lambda-dead-letter/

I have resolved it, set below path.
export NODE_PATH=/usr/local/lib/node_modules