Yes, definetly a White's tree-frog, and what a way to acquire a frog! I think you're doing good for right now, something you could do since it appears underweight, perhaps buy wax-worms which are high in fat and coat them in a frog-safe calcium and vitamin powder so he can get back the nutrients he's probably lost from being there. White's are one of the types of frogs that could live in a group, but you would have to quarantine any animal you attempt to add to the enclosure as they could be harboring diseases which are not only hard to cure, but could also spread to the original animal with disastrous results, not to mention you would have to get a bigger enclosure, as the recommended size for two White's tree-frogs is a 20 gallon tall enclosure, but of course bigger is better. Here's a few good care-sheets to help get you started:

http://www.frogforum.net/content.php...toria-caerulea

http://www.reptilesmagazine.com/Frog...tion-and-Care/

http://www.theamphibian.co.uk/whites...care_sheet.htm