Frank McPherson noted here a year ago that:
This mobile app search required the word “download” to precede an app name to increase the changes of correctly finding it in the appropriate app store. It looks like Google has change this process to be a tiny bit simpler in the intervening months. App searching is a bit hidden, however. Here’s how you do it:
1. Point your Android or iPhone browser at google.com
2. Tap the “more” link in the upper right side of the display
3. You will see a “tabbed” window like the one above with “Search” selected
4. Tap the “Apps” icon on the far right of the second row
5. Type in your app search term (see the screenshot immediately below)
Your results (see final screenshot) will only display apps from the appropriate app store. If you search on an Android phone, only links to apps in the Android Market will appear. If you search on an iPhone, only apps in the iTunes App Store will appear.