A sheriff is visited by Federal agents who are hunting an alien that has crashed in the hills ? an alien that can shape shift into any form. One by one people disappear and he must find and kill the creature to save his town.

Logline is a little too wordy and some of the information is unnecessary

You could try something like:

"A local sheriff teams up with two federal agents to track down a shape-shifting alien responsible for the disappearance of several members of his community... including his fiancee'!"

I kind of added the last part to raise the stakes.

Who is the protagonist? The sheriff or one of the agents? Writing it from his POV will be helpful.
Is "shapeshifting" an important detail in relation to the role or event or goal?
Is "crashing in the hills" important?
Or "visited by"?

Richiev captured your idea beautifully

but it's one sided fundamentally, and reads like:
"a local sheriff must team up with federal agents to kill a shapeshifting alien...."

the motive of this alien is unknown
In your original version people are disappearing one by one, not killed. "what the antagonist wants" is needed to establish the stakes.
Also it needs to be personal for the protagonist, something like "...when his beloved nephew goes missing..."

Its execution hangs entirely on your screenwriting ability

good luck music1358

When a shape-shifting alien kills several townsfolk, the local sheriff must team with a couple, not-quite-by-the-book, Federal agents to track and kill the thing.