The most common and most likely answer to this crossword clue is the 12 letter word POLTERGEISTS
I've seen this crossword clue in The Guardian
P
O
L
T
E
R
G
E
I
S
T
S
Buddy explains!
The straight part
We know that "they might move furniture" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they might move furniture = poltergeists.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POLTERGEISTS mean?
POLTERGEISTS noun- An unseen ghost which makes noises and causes disruption, especially by causing physical objects to move or fly about.