I agree with Shog9, and Journeyman Geek You can "ask" for a account to be suspended, but the answer will typically be "No" or "We ..." (or I) "...will investigate more into it." But sometimes it gets thrown a pile of look at later claims and suggestions, and most accounts requested to be suspended aren't unless the claim is stated up-and-out, or more and more people are flagging the account, so if either of those are true, than it will happen, but if its like 2 people who flag that account, most of the time it won't happen.
As being a admin of one site, and a moderator of a few others (mostly game sites), you go through a lot of claims and flags that mostly aren't true. So a lot of them assume the flag is useless, or inaccurate.
So to answer your question fully, yes you can ask a moderator to suspend an account, but I would not anticipate it to be very quick, nor for it to happen at all. But, go for it, if you have solid proof of it, and can present enough of it to a moderator (or admin), than they have to do something because you presented them enough information to prove the the flag was accurate, and is useful.