Depends on what kind of riding you want to do. If you are interested in road riding try the Pittsburgh Cycling meetup group. They organize all kinds of rides in and around the city for roadies that range from short rails to trails rides to more advanced, longer, touring rides.
If you are more interested in off road, try Pittsburgh Off Road Cyclists. Again, they gear some weekly rides for beginners specifically as well as more advanced rides for experienced riders. You can find both at www.meetup.com.
Otherwise, just get your butt some hours in the saddle daily. Try to meet some more experienced riders and take some rides with them. You'll be suprised at how quickly that you can build strength and confidence just doing those two things alone.
Good luck, and welcome!