The New Practical Reader is this list yes? http://www.skritter.com/vocab/list?list=list12

First, click the big green "Study textbook" button at the top left.

A dialogue box will pop up, select 'Lesson 15', and click "Begin studying".

If you click the show button, it'll show the character until you start writing.

If you hold the show button down, you it'll show you the stroke order too. But it'll still disappear when you start writing.

The reason for this, is that the thinking here is that if you are only tracing a character, you wont be putting it into your memory. It is much better to force yourself to memorise bits. That's why the character disappears.

If it is simply that the characters you're attempting are too difficult and are impossible to memorise (eg made up of lots of different parts), then why not start at the beginning of the textbook? Or perhaps study some of the list of radicals? Give you a better basis on which to attempt the harder characters.

Most harder characters are made up of simpler characters or radicals, and they are much much harder to do if you don't recognise the constituent bits.

that's the way it works on Skritter, there's no tracing option, and here's why:
http://www.skritter.com/forum/topic?id=79730505#79730725

one way to get help is to look at the bottom left of the screen, where there usually is a component breakdown of the character:
http://screencast.com/t/XdZ3aOaA

(and what @Byzanti said)

also James's suggestion here might help:
http://www.skritter.com/forum/topic?id=15151512#15219092