I have set up facebook LIKE box on my web page by copying code from facebook developers site.It works but on box i want to change "Find us on Facebook" line to something else and my question is how? :)
The way to do this is to loaded the appropriate SDK files. When you are referencing the JS SDK, all you have to do is define the language. Take a look at this documentation page (scroll down to "Changing SDK Language").
Depending on how you are loading the SDK (synchronous or asynchronous), you'll have to find the reference to the SDK's URL. It will look something like this:
//connect.facebook.net/en_US/sdk.js
What you have to do is change the en_US part of the URL to whatever locale you desire. A list of supported locals can be found in this XML file.
For example, here is the URL to load the Hebrew version of the SDK:
//connect.facebook.net/he_IL/sdk.js
^^^^^