My pleco is L001 and common pleco.
According to the data on Planet Catfish, L001 is omnivorous requiring both vegetable and meat. They suggest:
Lettuce, Peas, Frozen Spinach and any prepared food that reaches the bottom. Larger fish enjoy prawns or pieces of freshwater trout. Algae (especially soft brown) will be eaten immediately.
For "prepared food" I strongly suggest
Omega One Veggie rounds. This has algae/kelp but also whole fish. It also has no additives so it is more nutritional than many similar foods.
The common pleco,
Hypostomus plecostomus...When young it naturally feeds on algae, crustaceans, insects, small worms. As it matures it eats less and less algae. In the aquarium, it accepts most prepared sinking foods; algae/spirulina/kelp foods should be included. Frozen bloodworms, shrimp; live worms, insect larvae, brine shrimp. Vegetable matter such as zucchini, yam, driftwood, cucumber may be offered. Here again the Omega One Veggie Rounds will be ideal as a basic food, with all the rest as treats.
And as someone pointed out, plecos must have real wood in the tank to graze; they "eat" this not as nutrition but for the bacterial benefits to their digestive tract.