Leeks aren't ready for harvesting until autumn at the earliest, so they should still be small if you planted them this year. Did you sprinkle fertiliser around when you planted them? It sounds as though they failed to get going. When you plant them, make a 4 inch hole, drop the baby leek plant in and water to settle the soil around them. Don't fill in the hole, let the rain do this. Keep them weeded and watered. Plant at least 6 inches apart in May/June.