I made use of a website called MeetUp.com. I am actually an organizer of one of the Gay MeetUps here in San Diego.
When I first came out recently I was totally alone and an outsider in the Gay Community. I had no gay friends still with me so I was quite alone and isolated.
So, a coworker of mine introduced me to MeetUp.com where people can get together to plan 'MeetUps' with people of similar interests. For him it was a French Language MeetUp. For others it's a sports or activity MeetUp. For me, it was a Gay Singles MeetUp. From this web site I have made many friends and two possibilities for a relationship.
For socializing one's self it is perhaps the most powerful tool I have ever encountered. It is NOT a Match.com or a Grindr, it is merely a place where folks of like interest can plan face to face Meetups.
Also, for friendships, do not limit yourself to just 'Young Adults'. If we lived closer I'd be your companion for shopping, movies, games, concerts, etc. I'm actually a lot of fun for a middle aged person and I'm surprisingly well versed in current youth culture. I keep up with things, best I can. So don't limit yourself age wise.
http://www.meetup.com