Blueface angels are among the most reclusive of the family. As they grow, they tend to become more outgoing, but be prepared for this fish to hide much of the time. After they are settled, they should become aggressive feeders. One's I've kept would devour algae sheets, angel formula with sponge, things like mysis shrimp, Marine Cuisine, Emerald Entree, chopped clam, pellets, frozen plankton, etc.. Give it a good variety of foods. If it's a small specimen, make sure it is not being pestered by anything (e.g. the tusk).
Give it some time and feed regularly. If it's an otherwise healthy fish, it should start eating soon.