As Allen indicated add water to the suction strainer bowl. If this doesn't work it's almost certainly a gasket leak in the cover or one of the o-rings in the pump assembly. Check to be sure they are all clean and there's no crud in the groove. Lube them with a very small amount of silicone pool lube, take care not to stretch the o-ring. Unless you have an extraordinary lift or long run you should get at least a small flow into the pump almost immediately after you fill the bowl. And remember the pump is not designed to run dry for long periods of time. Water cools the seal assembly.
If you have an air leak and just can't find it try this. Hold a hose over each component so the water covers the potential leak sources. If you notice a change in the sound of the pump you've found a leak source.
I hope this helps.
Chris