I recently bought 3 neon tetras and out them in the tank with two older gouramies that were monsterous to them. It be like putting a shitzu dog next to a great dane. But the tetras did fine(two of them died though for unrelated causes =/), but they held their own with the bigger fish.

Check around, move around the gravel. I noticed the two of them went missing then discovered that they were dead. =/ Hope it turns up better for you