Walk up and start talking to people! Try your hardest not to be awkward or shy about it, and don't be creepin', but if you, say, see someone cosplaying from the same series, or wearing a button from a series you like, etc., walk up, compliment them on whatever it was that caught your eye, and see if you can strike up a conversation about whatever it was. If you hit it off, great! Introduce yourselves, maybe exchange contact info, and keep in touch the rest of the con and after the con. If not, oh well! there's tons of other people out there!
Also, events are a good way to meet people. Waiting in line? Talk to the person next to you! Sitting in a panel? Talk to the person next to you! Sitting in the karaoke room? Talk to the person next to you! Talk to artists that you like their work. Talk to people at gatherings from series you like and/or are cosplaying from.
It takes a bit of work, especially if you are shy, but there are tons of opportunities to meet people at cons, so take advantage of them (the opportunities, not the people, lol...see the "don't be creepin'" above).
Anywhere where you are with the same people for an amount of time, like in line (reg, Masquerade, Musicfest, panels, etc.), between karaoke songs (though the chair setup at Fanime isn't as conducive to talking as it is at cons with a table setup...not that I dislike the chair setup), etc., or places where people with similar interests gather (meetups, game room, AA, etc.) are the best places to meet people, because you are either stuck with them for however long the line is, or you know that they have similar interests as you (say, you are really into Pokemon, and they are at the Pokemon gathering decked out in Poke gear).
Also, talk to cosplayers about their costumes, even if you don't know what series they are from. Ask them about it. Strike up a conversation about possible mutual interests ("oh, you're cosplaying from Legend of Mana, some old JRPG? I've never played it, but I used to be really into Chrono Trigger back in the day. My fave character was Ayla. Do you like Chrono Trigger?" and go from there)
Observe basic social niceties, don't get too personal, too physically close, etc., make sure you don't smell, come off as overzealous, or overbearing, or like you're hitting on them, etc., and you should be fine. Also, if someone doesn't respond favorably, it might have nothing to do with you, and they might just be busy, tired, having a bad day, etc., they may be perfectly nice but shy and come off as rude, they might just not like people (like me! If you see me and I don't seem overly interested in a conversation, it's probably just because I don't like to talk to people very much, so don't take it the wrong way! People tell me that I seem unapproachable, but once I warm up to you, I think I'm nice enough

), etc. etc., and it might have nothing to do with you, so don't get discouraged. there's how many tens of thousands of people at this con every year? I'm sure that -someone- will want to be your friend, you just have to brave enough to find them.
