Magento 2.1.1 How to load Order with Increment ID using OrderRepository object

Magento 2 uses Service Contracts for retrieving and saving objects. In Magento this layer is formed by Repositories, which are managers with get() and save() methods. This keeps user code away from Model calls. Don't call model methods (like load() or save() or loadByIncrementId()) directly, they are being deprecated as custom code should use the Service Contracts. Also, don't use the API from within Magento like Khoa is suggesting, it does not make sense. The API is for connecting Magento with other systems.

Inject OrderRepository and SearchCriteriaBuilder in your constructor:

private $orderRepository;
private $searchCriteriaBuilder;

public function __construct(
        \Magento\Framework\App\Helper\Context $context,
        \Magento\Sales\Model\OrderRepository $orderRepository,
        \Magento\Framework\Api\SearchCriteriaBuilder $searchCriteriaBuilder
){
$this->orderRepository = $orderRepository;
$this->searchCriteriaBuilder = $searchCriteriaBuilder;
parent::__construct($context);
}

And in your function:

$searchCriteria = $this->searchCriteriaBuilder
    ->addFilter('increment_id', '000000001', 'eq')->create();
$orderList = $this->orderRepository->getList($searchCriteria)->getItems();

// $orderList is now an array of Orders with this incrementId, which is just one order obviously

/** @var \Magento\Sales\Model\Order $order */
$order = reset($orderList);
// Your logic here
$order = $this->orderRepository->save($order);

Official Magento PHP Developer guide on magento.com

Code by Mulderea on github

As far as I know, we should use \Magento\Sales\Api\Data\OrderInterface.

/** @var \Magento\Sales\Api\Data\OrderInterfaceFactory $order **/

protected $orderFactory;

public function __construct(
    \Magento\Sales\Api\Data\OrderInterfaceFactory $orderFactory,
    ......
) {
    $this->orderFactory = $orderFactory;

}

Load order object by increment id:

$this->orderFactory->create()->loadByIncrementId('00001952-42');

[EDIT] should try with service contracts. Try Jacco's answer.