Launching a game is hard. I get it, trust me. Finding an audience of receptive players and approaching them in a novel way is lots of work. Keeping them interested is even more work. Sometimes you want to be blunt and just tell people where to look.
There are a lot of ways to do this, but let me tell you what not to do: Don't randomly approach somebody on IM with a new/unfriended account and send only a URL. Because you know who does that? People who want to sell me ¢14l|$, that's who. If I get an unsolicited IM from an unfamiliar account and it's just a URL, do you know what I do? I block that account so it never bothers me again.
You know what I absolutely don't do? Click on the link. That's because, given its dubious source, it's likely to be an eyeball-stabbing fiesta of horrific web design at the very best, and thoroughly infested with malware at worst.
But there's another reason not to take a blanket approach to pinging people on IM that you should consider. Know your audience, dude. If you're taking the time to reach out to people one at a time -- or however many you can IM with at once -- then you have time to figure out who those people are, and whether they're receptive to what you have on offer. Let me give you a hint: if you are considering IMing me from an in-game account by way of introducing me to your game, I am not receptive to your advances.
If you are a friend or well-known colleague of mine, you will get a warm response from me if you approach me as yourself and say, "Hey, Andrea, I made this thing, take a look." I promise this is both cheap and effective.
If you don't actually know me, you probably need to rethink your approach to launching. I'm not a marketing vehicle, I'm a person. More, I'm a person who hasn't been an active or vocal player for any game in years, literally years, and who has already made my wishes regarding unsolicited trailheads very clear in the past. I've written about this exact problem with email before, and less than a year ago. (There must be something about September.)
But hey, if you want to be friends, then hop on in to the ARG SIG chat room and say hello. Once I get to know and like you, I'd probably be perfectly happy to help you launch your game.