I can't find my fish!?

Ok so I set my 10G tank about 12 weeks ago. I had a few guppies and catfish and tetras in it. Then my guppies died/ got eaten. I bought a Plecostomus that bottom feeds and now I can't find him. I've looked under the ornaments, filter, heater, rocks, plants, everywhere! He's the biggest fish in the tank. I haven't seen him for weeks now. If he was eaten wouldn't I see some kind of remains? Or even in the filter. I have a lid on the tank so he couldn't jump out. I looked behind the tank to but he's not there.