How to pull all emails of the site members in og invite new members?

I have og installed in my drupal site. In the group detail block there is a link of invite new members. On clicking this link a form appears Where I have to enter email addresses manually.

Basically the idea is that I want to add a field in the og_invite_form and search for the users members using their names. And then that user's email address should display in the email address field. If someone have some idea then please tell me.

Thanks in Advance...

I was mistaken, it is actually the OG Username Helper module that adds the autocomplete field to the invite page.

And still if you install the RealName module it lets you type the firstname or lastname of the user and it will place their username in the textarea below. Make sure you give the appropriate permissions to the desired roles.