Selenium with PhantomJs and NodeJs

i created a project with Express, and now i try to run selenium code with Phantomjs.

I have:

var app = express();

var webdriver = require('selenium-webdriver');

var driver = new webdriver.Builder().
   withCapabilities(webdriver.Capabilities.phantomjs()).
   build();

but when i try to run i have this error:

path/node_modules/selenium-webdriver/phantomjs.js:72
    throw Error(
          ^
Error: The PhantomJS executable could not be found on the current PATH. Please download the latest version from http://phantomjs.org/download.html and ensure it can be found on your PATH. For more information, see https://github.com/ariya/phantomjs/wiki
    at Error (<anonymous>)
    at findExecutable (/home/antonio/node_modules/selenium-webdriver/phantomjs.js:72:11)
    at Object.createDriver (/home/antonio/node_modules/selenium-webdriver/phantomjs.js:108:13)
    at createNativeDriver (/home/antonio/node_modules/selenium-webdriver/builder.js:43:24)
    at Builder.build (/home/antonio/node_modules/selenium-webdriver/builder.js:96:18)
    at Object.<anonymous> (/home/antonio/projectNode/ExpressProject/app.js:18:4)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)