Nearly everyone with LR has these stars, and it is quite rare for someone to get a problematic species. Not impossible, but really quite rare. Asterina stars are a normal component of a reef tank. I have never heard them pose a risk to clams.
I would assume they are innocent until proven guilty. In all likelihood, you have a harmless species as does most everyone else. Keep an eye out, but I would not personally recommend a specialized feeder to erradicate something that may not (and is most likely not) any problem at all. Nor would I recommend hunting them down manually. That simply will not work. Very cryptic and quick to reproduce, you could take a lot of the joy out of the hobby real fast.
I have loads of these, and report no problems. Most people report no problems. Of those that cause issues (and number of arms, size and color are no way to identify them), eating coralline algae appears to be the most harm they cause. Far fewer people report issues with soft corals. And even more rarely is an SPS muncher.
For the most part, these are eating microbial/algal films, which is why you find them on clam shells, glass and rockwork. So watch them, but I wouldn't assume you have a problem.