First of all I want to thank you guys for helping me identify my eel. I haven't felt this kind of help in a small community anywhere else.
Now for the tetra's we had a dissappearing issue when we had a rainbow shark. We ended up getting rid of the shark and getting tetras till we had 20. Now we're down to 12. I currently have 3 swordtails, 2 loaches, a small brisslemouth pleco and a larger pleco that survived. Plus 2 eels, one that was answered here and another is a zigzag eel.
Am I having a problem with hiding spots? I know I don't have enough plants. I'm thinking of getting more moss and covering the area under the wood structure on the right.
Or are they getting sucked up the filter? I thought this but couldn't find any evidence in the filter system. Any advice would be fully appreciated.
Here's the pleco I'm questioning. 
How long have you had these neons and what are your current water parameters?
Neons tend to be mass bred/produced now and aren’t always the healthiest when they arrive in the pet stores. So if they’re new, they may just unfortunately be dying and then your other fish may eat the bodies before you find it.
Similarly, if water parameters aren’t great they could be dying from that and same end result.
I doubt your pleco is catching and eating any neons. If any of your fish are likely culprits, I’d think its the eels, esp since I believe they’re nocturnal hunters? But I’ve never kept eels myself and don’t have much knowledge regarding that.
Edit: I just went to see your other post and it appears the other “eel” is a bichir. If it is indeed a fish eating your neons, that’s the likeliest culprit
You're 100% right! I found the culprit when I noticed just now in the middle of the night my tetras were scattered. I followed along and this bastard just snatched one up in front of me. I have to sleep so I'll be bagging him tomorrow and returning him.