Using token in page.tpl.php? I downloaded the social media module and I found this token: [socialmedia:sm-twitter_username]. I want to show it where the Read more / Add new comment section is, under an article. Since I can't find a block that is for that sections how can I just insert it into the code?
The Read more link is added by node_build_content(), while Add new comment is added by comment_node_view(); other links like those can be added by any module implementing hook_node_view().

So, to answer your question, there aren't theme regions you could use to add links where you see Add new comment, and you don't add them in page.tpl.php. You need a module implementing hook_node_view(), for example using the following code.

function mymodule_node_view($node, $view_mode, $langcode) {
  $links['socialmedia_twitter'] = array(
    // Depending on what the token returns, you need to use one of these lines.
    'title' =&gt; token_replace(' [socialmedia:sm-twitter_username]'),
    'href' =&gt; token_replace(' [socialmedia:sm-twitter_username]'),

    'attributes' =&gt; array('title' =&gt; t("Read !username's latest blog entries.", array('!username' =&gt; format_username($node)))),
  );

  $node-&gt;content['links']['mymodule'] = array(
    '#theme' =&gt; 'links__node',
    '#links' =&gt; $links,
    '#attributes' =&gt; array('class' =&gt; array('links', 'inline')),
  );
}


Rather than calling token_replace(), I would look at the module code, and see which function generates the token, and use it instead of calling token_replace(), since you are replacing a single, static, token you already know which one it is.
In any case, you need to check the code implemented by that module, as some token require an extra parameter passed as $data; without that, they don't work, or they don't produce the expected output.

In a theme, you would implement hook_node_view_alter().