I'm using porto theme too,
To edit the header I changed the header.phtml in Smartwave Module. Overwrite that to your custom Module app/design/frontend/Smartwave/porto/Smartwave_Porto/templates/html/header.phtml
This is the child for search area:
<?php echo $this->getChildHtml("top.search"); ?>
the line depends on the header_type you are ...
i went into the same issue suddenly. tried something no help.
reindex not help.
rm ibd then reindex still not help.
reset the db not help.
mysqlcheck --repair db not help.
all stucked at the issues of two tables doesn't exist. but when i want to create they are existed. inside phpmyadmin, the tables are there but click on it saying the tables not existed.
You can change the following settings and verify the search again.
please login into admin and go to the below path
store-> configuration -> catalog -> catalog -> catalog search
Set the Minimum Terms to Match to 100%
run the indexer command from your Magento web root.
and verify the search again on the frontend.
more information ...