Node.js cannot find module

I have 3 js files:

• app.js
• server.js
• utils.js

There is express server starts in server.js. app.js call server start from server.js. app.js is in root directory and there also is a src directory with server.js and utils.js. When I'm trying:

var utils = require('utils');

In server.js I get error:

Error: Cannot find module 'utils'

Why? utils.js and server.js are in the same directory.

Thank you.