Portanto..
<?php
$db_host = "localhost";
$db_user = "root";
$db_pass = "";
$db_name = "clientes";
$conn = mysqli_connect($db_host, $db_user, $db_pass, $db_name);
$pesquisar = filter_input(INPUT_POST, 'pesquisar', FILTER_SANITIZE_STRING);
$result_clientes = "SELECT * FROM clientes WHERE nome LIKE '%$pesquisar%' OR contato LIKE '%$pesquisar%' OR celular LIKE '%$pesquisar%' OR empresa LIKE '%$pesquisar%' OR endereco LIKE '%$pesquisar%' OR numero LIKE '%$pesquisar%' OR cidade LIKE '%$pesquisar%' OR estado LIKE '%$pesquisar%'";
$resultado_clientes = mysqli_query($conn, $result_clientes);
?>
<!DOCTYPE html>
<html lang="pt-br">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="css/bootstrap.min.css" rel="stylesheet">
<link href="css/estilo.css" rel="stylesheet" type="text/css">
<title>Clietes - Schuster</title>
</head>
<body>
<div class="container theme-showcase" role="main">
<div class="page-header">
<h5>Pesquisa de cliente</h5>
</div>
<div>
<div class="row">
<table class="table">
<thead>
<tr>
<th>Nome</th>
<th>Contato</th>
<th>Celular</th>
<th>Empresa</th>
<th>Endereço</th>
<th>Número</th>
<th>Cidade</th>
<th>Estado</th>
</tr>
</thead>
<tbody>
<?php while($rows_clientes = mysqli_fetch_array($resultado_clientes)){ ?>
<tr>
<td><?php echo $rows_clientes['nome']; ?></td>
<td><?php echo $rows_clientes['contato']; ?></td>
<td><?php echo $rows_clientes['celular']; ?></td>
<td><?php echo $rows_clientes['empresa']; ?></td>
<td><?php echo $rows_clientes['endereco']; ?></td>
<td><?php echo $rows_clientes['numero']; ?></td>
<td><?php echo $rows_clientes['cidade']; ?></td>
<td><?php echo $rows_clientes['estado']; ?></td>
<td>
</tr>
<?php } ?>
</tbody>
</table>
</div>
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script src="js/bootstrap.min.js"></script>
</body>
</html>