I have thousands of LinkedIn connections and I want to be able to send a message only to those in a specific city to let them know about an event. Is there an easy way to do this? I can send them one at a time based on a search filter, but it's taking too long.
There are only two ways to do it.
You could just post an update on your feed saying, "hey everyone I'm headed to [conference] on [date] in [location]. Let me know if you're around and we can meet up!"
That will at least get to people that check in on Linkedin occasionally.
The way your doing it now (manually)
Linkedin made it impossible to message multiple people at a time without manually adding their names (or clicking each person), one by one. You can't paste in a list of names like you can in email. You have to put in a single name, click the profile that pops up, then put in the nest name, etc.
In addition to posting an update on LinkedIn, you want want to consider creating a LinkedIn Pulse to promote why you are doing an event there. LinkedIn Pulse are typically articles individuals create but if you think in terms of thought leadership, you may attract people on LInkedIn.