None of the wordpress.com urls contain "www". The correct url for your blog is
This blog is in The Silver is the New Black theme. I just put that same theme up on my test blog and used icon 13 on the visual rich text editor and inserted a <!--more--> tag with no problem. The tag does not show until the post is published and once it is published the tag works only while the post is on the front page, exactly as would be expected.
Perhaps these instructions will help:
Using the "read more tag" to split long posts
If you follow the instructions and still do not get a "read more" tag in the post on your front page then you may have a technical problem. If this is the case you will need staff help. You can use this link during support hours (9-5 PM on weekdays) http://wordpress.com/contact-support/