Where should I go in Atlanta to network with other actors, casting directors etc?

Quality acting classes from respected instructors are probably the best way. So a good weekly acting class is a start. Also attending workshops and seminars.

Check out film festivals and other cultural series - attend the talk backs and lectures they offer. Volunteer at these events and at local theaters.

Contact local film schools and ask how they find actors for student films and check those sources.

Don't forget about social media - follow local industry professionals. Follow up with the people you meet at various events.

It's not like going to a party to meet people. You network by going to a good acting school, where you will meet other students as well as instructors. You network by getting experience in indie films and community theater, even by auditioning. The point of networking is NOT to get connections to get you work. The point is to impress them with your talent, skills, and knowledge. But as Cogito said, no one will hire you just because you're good friends with someone. You need to be highly-trained and highly-experienced either way.

But while we're at it, there's not a lot of networking opportunities in Atlanta, acting wise. To make real connections, you'd need to be where the industry is. In other words, where everybody works. That's LA, with NYC right behind.

Unless you've had years of top-quality training and experience, and have a really good agent, there would be no point.