How to direct marketing initiatives for a Start up

We are a location based social network connecting like minded people. We are ready with our product and want to select a city to start marketing. Basic costs touch upto $5k a month just for marketing. We can not market in more than one city for now. For the city that we choose to market, we want to show the city specific data to the users who log in.

Question / Issue - Once we choose a city lets say ABC and start marketing, users from ABC will see data related to their city. But if a user from another city lands on our landing page(possible due to social media word of mouth), we will not have the city related data for this user. What information can we show this user from another city? Should we have a coming soon to your area? What if we are not able to detect the user location!

Thanks,
RS

The word of mouth is bound to happen only when there's enough traction and happy users in the city you're initially launching and if you're gonna pay $5k for marketing and you can't do it in more than one city then its totally okay to have a simple coming soon page for people from other cities.
Many services like Groupon initially began targeting a small, specific geographic location before gaining traction and by extension the interest of VCs and startup investors before moving into other cities.

IMO, take it one city at time, focus on building a brand there and then you'll be in the position to move to other cities but when you gain enough traction quickly move into other cities by raising capital(it'll be easier then, you can show VCs good numbers.)

I think, what Karthik said is correct and I suggest creating a landing page for other cities as well. In case the user selects any other cities, you can ask them to subscribe to your website if they want you to notify them when commencing your service in their city. This will also help you in signing up the first few users from that city.