Snape, just like the other Death Eaters, would have been alerted of Voldemort's return and position when Voldemort touched Wormtail's Dark Mark in the graveyard, yet he did pretty much nothing about it. Sure, he may have told Dumbledore that his Mark had burnt, but why couldn't he have Apparated Dumbledore to the place the Mark was telling him to go so that they could figure out what was going on? They had plenty of time to do so, after all, and could have easily stopped the duel between Voldemort and Harry in time.
First: Since this had happened during the time of the competition, the atmosphere was inappropriate for such a move. Imagine the panic that would've been produced by Dumbledore's leave from such an important event.
Second, Snape is supposed to be a Death Eater and not inform Dumbledore, as Dumbledore's plan later unraveled. A fellow former Death Eater lurking nearby, which was the case; seeing Snape, would've jeopardized the plan. However, whether this plan was ready and waiting for Voldemort's return or put later on, is unclear. But, still, it's a possible reason for Snape's inaction, if any.
Also have in mind that there was no indication (to the good guys) that Harry was taken to that place where Voldemort supposedly returned (from their point of view). If they didn't know the latter's plans to teleport Harry, how would they have rushed to the rescue?!
All of the possible available information, was Voldermort's return, and not Harry's teleportation to this latter's whereabouts. Otherwise they would've prevented disaster before happening and more bloodshed.
Whether Snape had the first point in mind or not, is yet unclear.
1. It would have been a reckless move