Why does this search query not work?

backticks are useful also, they protect your query syntax:

$contestant_query = "select * from `news` where `main_body` LIKE '%$_POST[search]%' order by `headline`";

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First and foremost take the essential step to add error_reporting(E_ALL) to the top of all of your PHP scripts and correct any notices that appear.  This will help you avoid using undefined variables or undefined indexes.  It will save you from a debugging mystery!

Next, print out the contents of $_POST like this, and be sure that it contains the information you actually want to search for.

var_dump($_POST);

Next, change your query to use the correct escape sequence.  The code snippet will probably be correct if you're using procedural MySQL. Note the use of the quotes around the array index?  You want to do that; you do not want to rely on PHP making changes to your script silently.  It's always better to write the code correctly.

Check the results resource from the query to see that the query actually worked.  Print any associated error messages.

If the query succeeded, print the number of rows.

If you did not find what you were looking for, use phpMyAdmin to inspect the data base tables.

$safe_search = mysql_real_escape_string($_POST['search']);
$contestant_query = "SELECT * FROM news WHERE main_body LIKE '%$safe_search%' ORDER BY headline";
$res = mysql_query($contestant_query) or die("FAIL: $contestant_query BECAUSE: " . mysql_error());
$num = mysql_num_rows($res);
var_dump($num);

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These are things you should be doing with every query, every time.  It's tempting to take shortcuts, and PHP is notorious for permitting sloppy programming, but in the interest of getting accurate results fastest, all of these basic steps play together in ways that set you on the right course.