My DS (15 months now) was exactly the same OP, and I was worried sick. At one point he ate virtually nothing for 3 weeks (he's done 2 weeks on another occassion). He did seem to eat very little, but he was happy and I kept him going on milk. He was just very busy doing other things - even now sitting down to eat is fairly low priority if there are toys to play with, rooms to run across and cupboards to empty.
We did blw (he refused spoon feeding). As well as fruit and veg I used to offer - fallafel, meatballs, pieces of cooked chicken, bits of ham, bread/toast with lots of butter (calories), bit of cheese, skinless sausages, those yoghurts/fruit purees in squeezy sachets, frozen Frubes (as ice pops), oatcakes, drop scones (good source of eggs as finger food), potato wedges, fish fingers, cheese on toast, sardines on toast. Most of this stuff sounds like junk, but I home made most of it. Dried fruit, rice cakes, savory biscuts (again home made without any salt, spread with cream cheese).
He did drop centiles yes, but was never a "bad" weight for his age and height. At 15 months now, he will take a spoon, if he can do some himself too. And he has the appetite of a horse!