The value of a messenger app is in its adoption by heavy users who grow to depend on it, and then invite more people. You need to find a niche, and then aggressively get some adopters. Then, find out what value-added features would make them happy. By aggressively recruiting, I mean that just making a free version is not good enough. There is so much noise and competition. You need to contact users in this niche and, if need be, "bribe" them to use it. I know one app in the truck driver space that went to truck stops and gave out free t-shirts and food to get truckers to download and try their apps.