Um... There aren’t any? There may be an evaporative vacuum system for the gas tank but I think that’s about it for vacuum. Because of the hybrid design, the engine can switch off any any time, killing vacuum. So the brake booster, for instance, is electric. There also aren’t any belts; the AC compressor, engine cooling fan and water pump are electric.
Well that makes sense. So if you suspect a vacuum leak where do you look on this car? Just the main air intake and throttle body? I have a p0171 which manifests itself at idle. At highway speeds everything looks great (MAF, O2, STFT). Seems to imply air leak. This is a gen 3 2013 Prius four.
I can't think where the Prius would use vacuum either. Someone like @Elektroingenieur, @TMR-JWAP, or @JC91006 would probably know for sure.
On third- and fourth-generation Prius cars, intake manifold vacuum is used by the evaporative emissions control (EVAP), blowby gas ventilation (positive crankcase ventilation, PCV), and exhaust gas recirculation (EGR) systems. The Repair Manual (more info), in the topic Engine/Hybrid System: 2ZR-FXE Intake/Exhaust: Intake System: On-Vehicle Inspection, has an illustration of the sixteen places to check for vacuum leaks. This is also linked from step 3 of the procedure for diagnostic trouble codes P0171 and P0172.