cannot find module 'passport-local' error

am using passport in node.js

in my app.js

var passport = require('passport')

require('./config/passport').boot(passport, config)

in passport.js

var LocalStrategy = require('passport-local').Strategy

run the app and i get this error message

module.js:340
    throw err;

error:Cannot find module 'passport-local'
      at Object.<anonymous> <F:\work\config\passport.js:2:21>

i install the passport in F:\work\node_modules.

even if i put the

 var LocalStrategy = require('passport-local').Strategy

right under the

 var passport = require('passport')

i still get the same error

any idea why?