I tried one of the more expensive LinkedIn accounts awhile back, contacted about 10 people that all had mobile experience (my company makes an iOS and Android app for higher education), and only got 1 response to my message.
I assume part of it is that my message was read by these people, but they looked at it as "spammy," even though I wrote it individually to each person and tailored the message for each person. I've gotten messages from random people on LinkedIn, and it's easy to feel messages on there to be spammy.
So having my time on LinkedIn essentially feel like a huge waste made me question LinkedIn. Is it that I used their email system, and I should have instead setup a phone call?
Perhaps I am communicating a job that is not particularly interesting? I think an iOS and Android app with web backend, using the tech we are using (native languages for the native apps, and NodeJS for web), would be fairly attractive to a variety of developers though.
 Note: I am not actively looking and do not have this indication set on my profile. All contacts I am referencing are purely passive pings.