Looking for circuit diagrams of current mobile phone chargers
What Dwayne says should be noted. Image search is an immensely powerful tool for this. eg try lithium ion charger schematic 

BUT, here is a source that is often useful that Googling may not easily uncover.

Digikey (amongst others) has an utterly vast quantity of stock and a range of components beyond reasonable belief. They also have a very good parametric and keyword search engine that allows you to use them as a technical reference library. (I also even but stuff from them occasionally :-).)

Here is the result of a Digikey search for - lithium ion charger, followed by selecting the "Evaluation and Demonstration Boards and Kits" subset. 

This gives 100++ evaluation and development kits - many are relevant to your query and many have links to manual wit full circuit.

Digikey - Evaluation and Demonstration Boards and Kits - Lithium Ion Charger

Here's one example MCP1631HV Multi-Chemistry Battery Charger Reference Design

Also:

http://ww1.microchip.com/downloads/en/AppNotes/01137A.pdf
http://www.atmel.com/Images/doc7801.pdf
http://www.ti.com/lit/ug/sluu439a/sluu439a.pdf  

and many more.