posting page title and content depending on custom field and/or value

I want to display the thumbnail, the title and the excerpt of a specific page on my homepage.
I created the custom field ‘Teaser’ with the value ‘teaser’ and thought a can do this by filtering these.

Now I’d expect a function like

post_page_title($key, $value)
post_page_excerpt($key, $value) and
pot_page_thumbnail($key, $value)

to directly address the desired field.

I can’t find a function that comes close to this.

Does anybody have a clue where I should go?

Shouldn’t be too much php, as I have only started to do this.