If the bunny isn't moving he's likely not going to make it. If you take him into the vet the vet can give him som subq fluids (fluids under the skin) to rehydrate him, he's probably dehydrated. Then if he starts moving around you can feed him, but if he won't take the food you trying to feed him will make him aspirate the formula, what are you trying to feed him by the way? It'd be best if a rehabber could take him in, but he doesn't sound like he will make it. Bunnies are really difficult, I just tried to raise one and it died, he was very dehydrated, I gave him subq fluids and all, karo syrup (try just a drop in his mouth), and he was taking some formula, but he was too far gone already when I got him, he passed away. Good luck.
Missing being a pet parent, but will be again some day when the situation allows it...Rest in Peace Willow my aussie girl-sept.19 2010, sweet Satin bunny Oct 1999-Jan 10 2006 and Tinsle chinchilla 2004-Jan.23 2008, Shiloh beagle dog June 23rd 1994-April 17th 2008, Grace chinchilla Dec. 26th 2003 -July 2008, Kit chihuahua Dec 1997-2009.