Use class \Magento\Customer\Model\ResourceModel\Customer\CollectionFactory for loading customers collection. Method addAttributeToFilter for filtering
protected $_customersCollection;
....
public function __construct(
\Magento\Customer\Model\ResourceModel\Customer\CollectionFactory $collectionFactory
) {
$this->collectionFactory = $collectionFactory;
}
....
$search = 'data to search';
$this->_customersCollection = $this->collectionFactory->create();
$this->_customersCollection->addAttributeToFilter(
[
['attribute' => 'email', 'like' => '%' . $search . '%'],
['attribute' => 'firstname', 'like' => '%' . $search . '%'],
['attribute' => 'lastname', 'like' => '%' . $search . '%']
]);