When a delusional shut-in discovers that his favorite webcam model has been kidnapped, he must utilize his detective skills to locate her before she becomes another victim of a rampant madman.

I liked the detective skills part myself, it leads one to wonder if the shut-in might actually leave his house to do the investigation.

Somebody beat you to it.
http://www.imdb.com/title/tt2503154/

I would avoid to use favorite porn webcam model in the logline.
That make the protagonist seedy and creepy.
A reluctant h?ro is common, but a main character who the spectator does not respect is a big NO, NO.

Kidnapped by a gang of sex traffickers, a lonely neurotic nerd must save his favorite web-cam girl from them.

Anti-hero?

"When a deluded shut-in's favourite wedcam model is kidnapped, he takes it upon himself to rescue her from ... "

How does he know it's a rampant madman who has her? Or is he just guessing?

"... a notorious serial killer."

The stakes are a LITTLE unclear - I went with a notorious killer, because he could have heard this on the news, and then the implication is that her life is on the line - but I presume he equates his infatuation with her as love, and that if he rescues her she'll be smitten with him as well?

I think the idea has legs, just want this logline to be more streamlined, and possibly to have those questions clearer in the logline.

I knew I had seen a similar logline somewhere.
Amazon Studio had a competition on scripts and the winner had a script based on the very same premises.
It is called: I think that Facebook friend is dead.
It is supposed to be in rewrite before shooting.
Here is the link:
http://studios.amazon.com/projects/5046

http://ncis.wikia.com/wiki/NCIS_(series)

Again...thanks for all the feedback everyone.

Actually, that's one of the scenes in my script. Him trying to convince the cops was one of my favorite scenes to write.