I was looking forward to tearing into some creatures with a few throwing spears that I found.

However, they only seem to work properly in VATS. When I throw them outside of VATS, they just disappear and don't seem to hit the target. Am I doing something wrong?

They can't be picked up if that's what you mean.

I think he means that after he throws them in real-time combat, they vanish without harming the creature it was thrown at.

To answer your question, you're probably missing. The throwing spears in real-time aren't very accurate. But I've been able to kill some things with the throwing spears in real-time. They do seem to disappear though once they leave your hand instead of providing an animation of their flight, which is strange...

What I mean is that I can't hit any enemies unless I use VATS. (they also disappear when I throw them)

EDIT: @Volundarkvioa thanks, yes I guess that's why it seems they are not having any effect, there is no throwing animation so they just disappear and the enemy is not harmed.

Would the accuracy of throwing spears be governed by Melee and STR?

The spears were a major disappointment for me, and only good in vats.

Yes, I was hoping for something that would pin enemies to the wall like Bioshock

Yeah, Fun times!

The railway rifle can pin body parts to walls

If you land a killing blow with throwing spear and close enough to walls it would implant body parts on it, but it only last for three second or so.

I would like to see the return of Railway Rifle, but I guess they drop the heavy wild west railway theme for whatever reason.

Man, do I ever miss that gun. CHOOOOO

I've never had much of a problem throwing those weapons, close in and hold the fire / mouse button then release.
Thrown weapons are more a sneak weapon where ordinary melee would cause problems, i.e assassination.
V.AT.s however gives some cool moments in game, when I stood on the railing in the freeside casino feel off entered it in mid fall, and knocked the targets head off before hitting the ground is one.

To bad it's not in New Vegas D:

Yeah, all throwing weapons (spears, knives, and hatchets) are affected by melee. I don't believe STR has any effect on how far they'll be thrown though.

Hmm ...I see them in flight and then hitting target in real time all right. I have lot of fun hunting geckos around Goodsprings with spears (all in real time, I newer use VATS). They also make good poison delivery weapon. That they disappear and can not be picked after use is bit strange ...and makes them not very useful weapon in general.

I play on PC if it makes difference.

Y'all should try the Improved Throwing mod http://www.newvegasnexus.com/downloads/file.php?id=35101
- does what it says on the tin