How many times per week do you ask your friends: “Where are you?” There is no doubt social networking on your mobile phone is a big opportunity. According to Emarketer, the size of this market is expanding fast. 800 million people will be using their phones as mobile networking devices by 2012. (It was about 82 million in 2007).

So, who's playing in this market? Who's worth your (limited) attention? Here's a few that might kick up some dust:

Sniffu. Really? That's one of the worst names I've heard in a while. While the name sucks, they got some things right. I like the value proposition. It makes immediate sense. I also like that they don't seem to be trying to do too much. Keeping it simple. Their “Safety” page clearly illustrates the big issue all of these companies face: “Do people really want other people to know where they are in real time?”

Where also just landed a partnership with Yelp (Article here) . They could be a player to watch.

Dodgeball is an established player in start-up terms. Odd name. Not certain I get it. On the positive side, they did some good work on the user interface to explain what it is. I think the experience can be improved by giving the user more control of the animations.

Loopt got their partnerships down. Last week, they did a deal with Yelp. This makes a lot of sense for established and new Yelp users. Loopt is in a good position to make some moves. It works on 80+ phones, which I think is a real critical factor to success.

Next2Friends: Decent design. I found it interesting that these guys are funded by Simon - a real estate company. Why? Well, they own a bunch of malls, so they might possibly be making a play for mall-rats. “I'm in the store! Come see me while i try on some new boots!”

Their “Proximity Tagging” uses P2P Bluetooth to connect and record relative matches to other users and businesses that you come into close proximity to. Smart play for a real estate company. However, they have to be careful with the user experience. Make it too commercially driven and they risk alienating users.

Zannel is all about life-streaming. Share your pictures and video. Unfortunately, they stuff the UI with Google ads. This ruins it for me. Sorry lads and ladies. That's not the way to go. Please, let's see less - not more - clutter.

Radar has done a really nice job on their interface. Smart and clean design. For many users, photos drives sharing. Radar gets it.

Plazes Back in 2007, I wrote a post about them here. I wasn't too happy about their user experience at the time. They fixed it and they just got acquired by Nokia last month. That means this is possibly the gorilla to watch. Coming out of Berlin, Plazes is still a bit German-centric and, as with all mobile social networks , that's a challenge if you live in Los Angeles (or any other US city).

If you do happen to live in the US, you might check out Platial. I just installed their iPhone application today and I'll be taking it for a spin at the Sunset Junction Street Fair tonight.

Another player in this space seems to be Brightkite, who seems to be in private BETA. I've not tried it yet, but I'll give it a run once I get access.

The real question is how all these players are going to scale. It's not going to be easy and we'll have to see what happens when Facebook and Google really pick up steam. Meanwhile, go startups!

There's no recession in social networks. In the last year, Twitter grew 343%, LinkedIn 193%, and Facebook 116% according to Nielsen. MySpace's growth has stalled at 1%.

It's worth pointing out that pure growth in registration numbers is not the only metrics that matters. Data on user activities such as page views, time spent on site, visit frequency, as well as member interactions and purchases are all important when you evaluate the value of these networks.

Engaging users over time has proven to be tricky. Yeah, you can build it and you might even be able to get people to register. But can you make them stick around? Many can't make it work and that's been an expensive lesson for many brands and marketers.

It's a challenge one of our teams are taking head on. Ryan Nash, Sara Apelkvist, Michael Jung, and Clayton Kjos are developing a new niche social networking site due to launch in January.

We can't wait to share our design experience with you when the BETA site becomes available in late January. Can we make you stick around?