Organic Groups: how to add an invite link?
I have recently used Organic Groups Invite module to add this functionality to a site. It will give you a "OG Invite Button" block that you can place on the user view page. 

Edit: Sorry the block wasnt included I had added it with a custom module here is the code:

/**
 * Implements hook_block_info().
 */
function og_invite_button_block_info() {
  $blocks['og_invite_button'] = array(
    // The name that will appear in the block list.
    'info' =&gt; t('OG Invite Button'),
    // Default setting.
    'cache' =&gt; DRUPAL_NO_CACHE,
  );
  return $blocks;
}

/**
 * Implements hook_block_view().
 *
 * Prepares the contents of the block.
 */
function og_invite_button_block_view($delta = '') {
  switch ($delta) {
    case 'og_invite_button':
      $block = array(
        'subject' =&gt; t('OG Connect Button'),
        'content' =&gt; og_invite_button_block_content()
      );   
    return $block;
  }
}


function og_invite_button_block_content() {
  //Get user from profile page
  $user_viewed = arg(1);
  $user_viewed_fields = user_load($user_viewed);

  global $user;
  $output = '';

  $query = db_select('node', 'n')
  -&gt;fields('n',array('nid'))
  -&gt;condition('type', 'group')
  -&gt;condition('uid', $user-&gt;uid);

  $result = $query-&gt;execute();

  foreach ($result as $row) {

    // Check if the user is already an existing member.
    $exists = db_select('og_membership', 'ogm')
      -&gt;fields('ogm', array('id'))
      -&gt;condition('gid', $row-&gt;nid)
      -&gt;condition('etid', $user_viewed)
      -&gt;execute()
      -&gt;fetchField();
    if (empty($exists)) {
      $name = $user_viewed_fields-&gt;field_name['und']['0']['value'];
      $output .=  '&lt;a class="orange_btn" href="/group/node/' . $row-&gt;nid . '/admin/people/invite-users/' . $name . '/' . $user_viewed . '"&gt;Invite To Your Group&lt;/a&gt;';
    }
  }
  return $output;
}


Some improvements could definitely be made like theming the link.

You will also want to add the name of the group to the button if the logged in user is the owner of more than one group.