instead of the command: pm2 start app.js
try this command: pm2 start ./bin/www

you should use the same line after the pm2 start as you have in the start script of your package.json file in the express app root folder

There some issue with digital ocean server.
I can start server with pm2 start app.js
monyrestparameters"
[PM2] Applying action restartProcessId on app [app](ids: 0)
[PM2] [app](0) ✓
[PM2] Process successfully started
┌──────────┬────┬─────────┬──────┬───────┬────────┬─────────┬────────┬─────┬──────────┬───────────┬──────────┐
│ App name │ id │ version │ mode │ pid │ status │ restart │ uptime │ cpu │ mem │ user │ watching │
├──────────┼────┼─────────┼──────┼───────┼────────┼─────────┼────────┼─────┼──────────┼───────────┼──────────┤
│ app │ 0 │ 0.0.0 │ fork │ 23428 │ online │ 5 │ 0s │ 0% │ 4.7 MB │ dev2rt987 │ disabled │
└──────────┴────┴─────────┴──────┴───────┴────────┴─────────┴────────┴─────┴──────────┴───────────┴──────────┘

0|app | server is listening on port 4000

but when I open server from browser. Request dont come to the server. I checked 4000 port its open and listening on the server.

For anyone having this issue, I solved it by appending some required node parameters.

Mine looked like this: pm2 start app.js --node-args="--harmony-destructuring --harmony_rest_parameters"

You may need to pass in some required arguments. Check package.json for a start script.

http://pm2.keymetrics.io/docs/usage/quick-start/#42-starts

I compiled my app.js using npm build then pm2 start public/app.js worked for me