With new Twitter API, you need to create API keys. 

Please follow the steps in order to create Twitter API: 

1- Go to https://dev.twitter.com/apps/new and log in, if necessary
2- Supply the necessary required fields, accept the TOS, and solve the CAPTCHA.
3- Submit the form
4- Copy the consumer key (API key) and consumer secret from the screen into your application
5- Click to "Create my Access Token" button
6- Copy the Access Token and Access Token Secret 

All the required infos will be entered to Theme Options > Contacts & Social

