There is a true saying: companies are bought, not sold. Meaning that if no one is interested in buying, you'll never be able to sell.
So you should do your homework and figure out some likely acquirers. Then, approach their business development department (using LinkedIn for instance to identify real individuals), and ask to talk about a potential partnership - not an acquisition.
Once in the meeting/phone call, show off all the great things about your site. If they are interested, they will let you know. How? If they call you back with not additional sollicitation on your side, they are interested.
That's a lot of uniques and in a very hot space (mobile). I'd imagine there are a lot of people that would have interest.
I'd identify 2-3 potential suitors and just give them a call. If you can't find a connection into the right person in the company through your network, just make your best guess ("VP of corporate development" in big companies) and go for it. It worked for me about a year ago.
If you can't think of a clear way to offer to be a "partner" then just be straight and honest with them. IMHO, the corp dev guys I've worked with have no issue with people getting straight to the point. They are in the business to do deals (i.e., buy companies), so they aren't put-off by bold entrepreneurs. The key is in the voicemail or email you send, make sure the 16M+ uniques and the mobile market are loud and clear....that will get their attention.
And never seem too anxious or excited, make sure they know you want the right deal, not just any deal....that will keep the valuation up ;)
I attempted to use business brokers twice in the past 10-years for a web businesses...it never worked...
I have seen "rain makers" effectively make it happen, but they aren't professional business brokers...just well connected people that for a small finder's fee open their Rolodex and make a few calls....
And once you find a real suitor...get a good M&A attorney involved...if they are good, they are very well worth their money....
UPDATE: Also, you gotta be careful with the business brokers. Some of them are scams (in my opinion). We got in deep discussions with one and they were "ready to sell our company to one of three parties via an auction model". Sounded great! Until the guy asked for a $15,000 non-refundable deposit via our Corporate American Express card. He wouldn't take another step without it. Apprarently there are companies out there that take the deposit, advertise your company, if it works great, if not great....they still make $15k. If you come across one of these, run, not walk away. A real, successful business broker will work for pure commission...or they aren't worth working with.
You have two options:
1) Hunt down someone who specializes in doing this, I don't know any well enough to make a referral but you can definitely find people who can help sell your business.
Also, feel free to drop me a line with the URL and revenue numbers.. I know people who are always interested in buying sites that are turning a profit.(javery ^at^ infozerk.com)
Find someone who has experience brokering M&A exits. Give them an ownership stake in your business, and you will have an experienced advocate to guide you through the process of valuing the business, finding and courting potential acquirers, and reaching the best price. You will pay a lot, but a motivated advocate can deliver more value than they take, just like a real estate agent.
Tom Lions of Faelon Partners Ltd has a pod cast at http://www.todaysbusinessradio.com/. His firm specializes in selling companies. Several of his pod casts address similar questions to the one you just asked. This may provide some insight into selling your business. I would recommend listening to “Mergers and Acquisitions”