how to get product thumbnail and product url in order confirmation email

you have to load product to get thumbnail and url .

    <?php $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$product = $objectManager->create('Magento\Catalog\Model\Product')->load($_item->getProduct()->getId());
 echo $product->getThumbnail();
echo  $product->getProductUrl(); ?>

//get image url

$imagewidth=200;
$imageheight=200;
$imageHelper  = $objectManager->get('\Magento\Catalog\Helper\Image');
$image_url = $imageHelper->init($product, 'product_page_image_small')->setImageFile($product->getFile())->resize($imagewidth, $imageheight)->getUrl();
 echo $image_url

I've tried this code myself, its working.

override vendor/magento/module-sales/view/frontend/templates/email/items/order/default.phtml and use this code in it:

<?php
/**
 * Copyright © 2016 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */

// @codingStandardsIgnoreFile

/** @var $block \Magento\Sales\Block\Order\Email\Items\DefaultItems */

/** @var $_item \Magento\Sales\Model\Order\Item */
$_item = $block->getItem();
$_order = $_item->getOrder();
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
?>
<tr>
    <td class="item-info<?php if ($block->getItemOptions()): ?> has-extra<?php endif; ?>">
        <p class="product-name"><?= $block->escapeHtml($_item->getName()) ?></p>
        <p class="product-name"><?= $block->escapeHtml($_item->getName()) ?></p>
        <p class="sku"><?= /* @escapeNotVerified */  __('SKU'); ?>: <?= $block->escapeHtml($block->getSku($_item)) ?></p>
        <?php if ($block->getItemOptions()): ?>
            <dl class="item-options">
            <?php foreach ($block->getItemOptions() as $option): ?>
                <dt><strong><em><?= /* @escapeNotVerified */  $option['label'] ?></em></strong></dt>
                <dd>
                    <?= /* @escapeNotVerified */  nl2br($option['value']) ?>
                </dd>
            <?php endforeach; ?>
            </dl>
        <?php endif; ?>
        <?php $addInfoBlock = $block->getProductAdditionalInformationBlock(); ?>
        <?php if ($addInfoBlock) :?>
            <?= $addInfoBlock->setItem($_item)->toHtml() ?>
        <?php endif; ?>
        <?= $block->escapeHtml($_item->getDescription()) ?>
    </td>
    <td>
        <?php
            $_product = $objectManager->get('Magento\Catalog\Model\Product')->load($_item->getProductId());

        $imageHelper  = $objectManager->get('\Magento\Catalog\Helper\Image');

        $image_url = $imageHelper->init($_product, 'product_page_image_small')->setImageFile($_product->getFile())->resize(100, 100)->getUrl();
        ?>
        <img src="<?php echo $image_url; ?>">
    </td>
    <td class="item-qty"><?= /* @escapeNotVerified */  $_item->getQtyOrdered() * 1 ?></td>
    <td class="item-price">
        <?= /* @escapeNotVerified */  $block->getItemPrice($_item); ?>
    </td>
</tr>
<?php if ($_item->getGiftMessageId() && $_giftMessage = $this->helper('Magento\GiftMessage\Helper\Message')->getGiftMessage($_item->getGiftMessageId())): ?>
<tr>
    <td colspan="3" class="item-extra">
        <table class="message-gift">
            <tr>
                <td>
                    <h3><?= /* @escapeNotVerified */  __('Gift Message') ?></h3>
                    <strong><?= /* @escapeNotVerified */  __('From:'); ?></strong> <?= $block->escapeHtml($_giftMessage->getSender()) ?>
                    <br /><strong><?= /* @escapeNotVerified */  __('To:'); ?></strong> <?= $block->escapeHtml($_giftMessage->getRecipient()) ?>
                    <br /><strong><?= /* @escapeNotVerified */  __('Message:'); ?></strong>
                    <br /><?= $block->escapeHtml($_giftMessage->getMessage()) ?>
                </td>
            </tr>
        </table>
    </td>
</tr>
<?php endif; ?>

and in override vendor/magento/module-sales/view/frontend/templates/email/it‌​ems.phtml and use:

<?php
/**
 * Copyright © 2016 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */

// @codingStandardsIgnoreFile

?>
<?php $_order = $block->getOrder() ?>
<?php if ($_order): ?>
    <?php $_items = $_order->getAllItems(); ?>
    <table class="email-items">
        <thead>
            <tr>
                <th class="item-info">
                    <?= /* @escapeNotVerified */  __('Items'); ?>
                </th>
                <th class="item-qty">
                    <?= /* @escapeNotVerified */  __('Qty'); ?>
                </th>
                <th class="item-qty">
                    <?= /* @escapeNotVerified */  __('Image'); ?>
                </th>
                <th class="item-price">
                    <?= /* @escapeNotVerified */  __('Price'); ?>
                </th>
            </tr>
        </thead>
        <?php foreach ($_items as $_item): ?>
            <?php
                if ($_item->getParentItem()) {
                    continue;
                }
            ?>
            <tbody>
                <?= $block->getItemHtml($_item) ?>
            </tbody>
        <?php endforeach; ?>
        <tfoot class="order-totals">
            <?= $block->getChildHtml('order_totals') ?>
        </tfoot>
    </table>
    <?php if ($this->helper('Magento\GiftMessage\Helper\Message')->isMessagesAllowed('order', $_order, $_order->getStore()) && $_order->getGiftMessageId()): ?>
        <?php $_giftMessage = $this->helper('Magento\GiftMessage\Helper\Message')->getGiftMessage($_order->getGiftMessageId()); ?>
        <?php if ($_giftMessage): ?>
            <br />
            <table class="message-gift">
                <tr>
                    <td>
                        <h3><?= /* @escapeNotVerified */  __('Gift Message for this Order') ?></h3>
                        <strong><?= /* @escapeNotVerified */  __('From:'); ?></strong> <?= $block->escapeHtml($_giftMessage->getSender()) ?>
                        <br /><strong><?= /* @escapeNotVerified */  __('To:'); ?></strong> <?= $block->escapeHtml($_giftMessage->getRecipient()) ?>
                        <br /><strong><?= /* @escapeNotVerified */  __('Message:'); ?></strong>
                        <br /><?= $block->escapeHtml($_giftMessage->getMessage()) ?>
                    </td>
                </tr>
            </table>
        <?php endif; ?>
    <?php endif; ?>
<?php endif; ?>