Composite design only helps for positive moment design at the middle of the member. And since for portal frames the controlling moments are negative and at the supports, you're losing the major benefit.
Are you asking about composite metal deck (Vulcraft VLI for example), or steel beams composite with the concrete slab? Both can be used in a moment frame building. Jed's comment is valid for the column to column girders, but the infill beams can certainly still benefit from being composite with the concrete slab.