I bought a rectangular knitting loom a while back, opened it up, tried it out, and then set it aside to move on to other projects. I just know that I put the hook in a bag with the project I was working on, but go figure, it’s gone MIA on me lol So, here I am, anxious to pick the loom back up, but I have no hook! So my question is, can I use a crochet hook as a loom hook, and if so, what size? (I’m a crocheter, so hooks are one thing I have PLENTY of 
) Thanks in advance!
Question about using a knitting loom
Hi and welcome to KH!
I googled around a bit and can find where you can use a crochet hook to help you get started but not sure on if you can use it the rest of the time.
I did find this site where she gives some ideas on the Knitting loom tool
There are several videos on youtube too
Basically bumping this up and hopefully someone else can give you a better answer 
No reason not to give it a try with crochet hooks. They may not ‘hook’ enough, but might still work fine. Just put a pile of them in various sizes next to you. If a larger hook doesn’t work well, try a smaller one.