There are two problems here: (1) Increasing the visibility of LW among minds which could be positively influenced by it. (2) Coordinating the already interested minds to meet at one point in the timespace.

You asked specifically about the latter, but I want to make it explicit that the former is a meta-strategy for the latter. The more people know about LW, the easier it is to get some of them to the meetup. (These is a chance -- although I wouldn't rely on it -- that with popularity big enough, someone else would organize the meetup.)

As a data point, the first meetups in Slovakia had between 4 and 6 people. And even that was because there were already 2 organizers (me and my girlfriend, and she did it partially to make me happy), and at that time there were no regular meetups in neighbor countries, so we regularly had one or two visitors from other country. It took more than a year to create a relatively stable community of about 10 local people. And I had to make some trade-offs; for example a few of them are not fluent in English, so we speak in Slovak, which excludes the potential foreign visitors.

I am saying this to prepare you not to be disappointed by smaller participation. On the other hand, there are a few possible strategic moves I have ignored so far (such as doing a LW presentation at a local university), so a better strategy could possibly bring higher participation.