sites = await Site.findAll({
  where: {
    [Op.or]: [
      'title', 'site_url', 'tags'
    ].map(key => ({
      [key]: {
        [Op.like]: `%${search}%`
      }
    }))
  }
});

SELECT * FROM `Sites` AS `Site` WHERE (`Site`.`title` LIKE '%min%'
  OR `Site`.`site_url` LIKE '%min%' OR `Site`.`tags` LIKE '"%min%"');