I work at LoopNet so I know a thing or two. First, it is indeed the largest commercial RE marketplace online so you never know what is going to pop up. A lot of my clients are Principles and they buy and sell a lot of property using LoopNet all the time.
Your best best is to setup a search and save your criteria so you get the email alerts of anything that matches your criteria.
@Steve S. Your are right in some regards to that point. Typically when agents or brokers get a listing they shop it around to their own private network of personal investors. If those investors all pass on it then it typically ends up on LoopNet and CoStar so they can market it to the rest of the world. But if LoopNet didnt work, then no one would be posting, right? So it all depends on your own personal investing criteria, really.
And from the listing agents perspective, LN is key to show your seller that you are generating broad exposure to find a buyer.