The Google Sandbox effect is an alleged restriction placed on new websites. The result is that a new site does not receive good rankings for its most important keywords and keyword phrases for few months.
This google sandbox checker tool helps you to check if your site is in google's sandbox for a given keyword. This checker tool has fields to enter the keyword, URL and to select Google's regional domain. On clicking Submit the tool tells you if your site is been placed in google's sandbox.
If you were to ask Google’s Matt Cutts, he would insist that the Google Sandbox is nothing more than an running rumour which some people have come up with to try and explain their own poor efforts at SEO. Google representatives have repeatedly announced that Sandbox phenomena is just a myth!! Now, what people assume to be the ‘Sandbox effect’ is usually a penalty slapped by Google for employing bad SEO practices...If you employ white hat SEO techniques (on-page and off-page); there is no reason why you won’t get indexed fast!
Google Sandbox is a technique to hide your URL from Google but you're doing SEO for this but it wouldn't be show up on google's search results.
Check your webmaster account if you don't have any message about quality issues, then you are probably sand boxed. Follow the recommendations above and your site will get back on track.
The Google Sandbox Effect is a theory used to explain why newly-registered domains or domains with frequent ownership changes rank poorly in Google Search Engine Results Pages (SERPS). In other words new websites are put into a “sandbox†or a holding area and have their search ratings on hold until they can prove worthy of ranking.
Best way to escape from sandbox is to target less competitive keywords. Websites that get into sandbox are sites which target highly competitive keywords. If you target less competitive keywords or long phrases then your chances of getting sandboxed is very less.