Search on specific content
You're looking for the Custom Search module.
This module alters the default search box in many ways. If you need to have options available like in advanced search, but directly in the search box, this module is for you.

Basic options
The module adds options to select:

which content type(s) to search,
which specific module search to use (node, help, user or any module    that implements search),
which input type to use (with Elements),
advanced criteria

For all these choices, there are options to switch between a select
box, checkboxes or radio buttons, and also customize the selector
label and the default - Any - text.
Advanced options
There are also options to:

change the default search box label,
add a default text in the search box,
add advanced search criteria,
change the default submit button text,
use an image instead of the submit button,
change the order of all the elements,
include some elements in a popup block,
add a filter to the results page,
show/hide basic and/or advanced search in the results page,
show/hide meta data in the results page,
multiple search paths


You can also achieve that by writing a custom module. Have a look at
Build a Drupal 7 Content Type Search Block in 5 Easy Steps