I use GroupMe; although it isn't laid out as "beautifully" as Path is, it's simple to use and you can share photos pretty effortlessly. I don't think it has as many bells and whistles as Path (I installed it once but then ended up deleting it because the utility was near zero) but it works great to have an ongoing conversation with a gorup of buddies. The thing I love about GroupMe is that you can create new groups and add different people according to the situation at hand; it's awesome for concerts, festivals, and shared events to keep track of everyone. The downsides are it doesn't have the longevity of something like a Path, and it's a battery HOG...make sure to turn off Push notifications or you're going to have a bad time. Also just to disclose, I don't work for GroupMe so not a corporate plug. I've also heard What's App is great although I've never used it myself.

Internet Relay Chat (I'm into simple solutions)

I really like using email for staying in touch, also works with groups.

But besides the fact that my friends aren't really into the whole tech thing (lot of them are still using their old non-smartphone) Inlining videos, photos and threading conversations is something I really like for such a software to have.

One other idea that comes to mind is that you could create a private subreddit on reddit.com and make it closed/invite-only. Reddit doesn't ask for personally identifying data.