Not all backlinks are displayed by Google or by backlink checkers
Link building is a very important aspect of SEO and it is useful to check that Google and other search engines have indexed any links you have built. Since search engines crawl the web at different rates, a particular link may be picked up by one search engine but not the other.
Most search engines have a ‘cached’ link under each search result that will show you the latest version of the page as seen by the search engine with a time and date of the last cache. This is useful in figuring out whether your link has been seen by the search engine.
Some search engines, such as Google, will only reveal a fraction of the backlinks it has indexed in an effort to combat manipulation of rankings via links. This makes it hard to get a complete picture of your site’s backlinks from Google’s point of view. Instead, other backlink checkers such as Yahoo SiteExplorer are used to estimate backlinks indexed by Google.
In summary, just because you can’t find a link in a backlink checker doesn’t mean it hasn’t been indexed. Also keep in mind that from an SEO perspective, both the quality and quantity of links are important, and link building is just one facet of any good SEO campaign. So use a backlink checker to get a sense of where your website stand against your competitors, rather than let it drive your campaign.