A few weeks back, Foursquare announced Swarm — a new app that aims to help track down your friends when you're out and about. Using Swarm, you'll be able to see which of your friends are nearby, even if they haven't checked in somewhere. You can also suggest plans to your Swarm friends, then text those that are interested in tagging along.
Swarm is a separate app from Foursquare (which is getting a revamp of its own very soon), so the feature set is different than what you're used to. New stickers will replace things like mayorships and leaderboards, making Swarm more about being social and less about the competition. You're also able to search back through your entire check-in history within the Swarm app.
Swarm is free to download and use, but keep in mind that you'll need a good set of friends also using the app to make it worthwhile.