"I'm going after Lupin." Harry says, as soon as Snape disappears around the corner, dragging the Marauder's Map out of his pocket and hurriedly tracking Lupin.
Ron wants to tell him that, no they're not doing that, but he gets it. With what Harry just found out about Black, Ron can completely understand why Harry has to go. Also, he wants to know why Lupin came after Scabbers.
Hermione must sympathise as well because she doesn't say anything against the idea.
They barely make it to Lupin's office in time to hear him shout an address. After convening and making sure they all heard the same thing – Harry's track record with floo powder being less than stellar – they throw what looks like the last of Lupin's powder into the flames and repeat the address in unison.