It is true that a large number of people are using mobile phones that has automatically increased the user base referring to Google's mobile search pagefor getting information. If you are a webmaster, you must be aware of the fact that running a mobile site and making it reach the audience is a difficult job.
Apart from having a different format from desktop site the mobile site has different management methods also. The latest Google Webmaster blog is talking about how you can make the mobile site available for users of mobile search. The blog is providing some troubleshooting tips that will lead to proper crawling and indexing of the mobile site.
In case your mobile site is not showing results of Google mobile search even after using the 'site:' operator, there might be following issues with the site:
There are chances of Googlebot not able to locate the website.
The crawler Googlebot must crawl the website before including it in the search index. If your site is newly made, you might not be aware of this thing. What you can do is, create a Mobile Sitemap and submit it to Google. The map can be submitted by using Google Webmaster Tools and the process is similar to what you do for a standard Sitemap submission.
If Googlebot is not able to access your site.
There are some mobile sites that don't provide access to mobile phones. If this is the case with your site, Googlebot will be unable to access it and thus the site will be unsearchable. The Google crawler for mobile sites is "Googlebot-Mobile". You have to allow any User-agent including "Googlebot-Mobile" to access your website for crawling. There are chances of Google changing the User-agent information without prior notification, therefore you should not check if the User-agent matches the "Googlebot-Mobile". Instead of this, you should check if the User-agent header has the string "Googlebot-Mobile". The verification of Googlebot can also be done by using DNS Lookups.
How to Verify if Google can recognize mobile URLs?
After the Googlebot-Mobile crawls the URLs, it is checked if the URLs can be viewed on mobile device. If the determined pages cannot be viewed on mobile phone, they will not be included in the mobile site index. The determination process is based on factors like DTD (Doc Type Definition” declaration. You should check if the mobile-friendly URLs' DTD declaration has an appropriate mobile format like Compact HTML or XHTML Mobile. You can get more information by going through Google's Mobile Webmaster guidelines.