- Verify that the site is up and running. A missing website will get taken out of search engine rankings.
- Is the site really missing? Do a site: command to find out. Check to see if pages are cached.
- Look at your Robots.txt file, if you have one. (A missing Robots file won’t derail your rankings.) If there is a line that only says “Disallow: /”) then you are telling the search engines not to read the site.
- Check the source code on your pages for metatags that say “Noindex” or “nofollow,” as these tags may tell the search engine to ignore the page.
- Check your root directory to make sure you don’t have an extra homepage named “home” or “index” or “default.” Also check that you don’t have an “index.htm” and an “index.html” competing with each other. A search engine (or any other browser) should only have one choice for a homepage or interior page.
- Check for Broken Links by using a Spider Emulator.
- Check your server traffic and logs to see if the site was down for any length of time. Every now and then, a site will be down at the same time the search engine comes to visit.
- Did you change your directory structure? It may take time for search engines to see it.
- Did you change from HTML to ASP, or from PHP to Cold Fusion? Essentially, you have a new site and need to tell Google that it is there.
- Did anyone file a DMCA (Digitial Millenium Copyright Request) against you for duplicate content? Normally, someone gets notified when this happens, so check the email address listed on the WHOIS lookup.
- Is the site content duplicated elsewhere? If so, the search engine may be listing the original content in lieu of yours.
Google Webmaster Tools also does a great job telling you if there are issues with your site, and even has a handy red flag to tell you if you’re been banned.
One of the top directives in SEO is not to panic, but it is hard not to panic if you can’t find your site on Google, Bing, or Yahoo, especially if the site had good rankings before. If you’ve been using black hat techniques, or got a lot of low value links with the same anchor text, or made a big change to your site, you can vanish from the search engines. If you still don’t know what has happened to your site, an SEO consultant may be in order, since a few hours of consulting time can uncover issues (both obvious and subtle) that can bring your site back from the search engine twilight zone.