Recently after Ramdan I see this site is not having much activity by some of the Moderators. One of the Mods is not even seen around, even while he was around he contributed little although earlier this year he was actively contributing quality content. Moreover there is a similar case for high rep users, So what is the reason behind this and how to increase Moderator participation?
The truth is that there was a notable spike in traffic duing Ramadan this year. Presumably people who are interested in learning about the sacred month turned to this site for information. After that time period, site activity simply returned to normal levels.
This site has 4 moderators. Normally beta sites are given three, so it doesn't hurt if one of them takes some time off for whatever reason. Of note, this site had far fewer flags in the last quarter than did Christianity and Judaism. The moderators are handling flags quickly and the workload does not seem onerous.
Remember that moderators, like all other participants on the site, are volunteers. They have obligations and responsibilities outside of the site and off of the internet. The same is true of high-reputation users who may chose to come and go as they wish.
The best way to encourage participation is to ask excellent questions. The next best way is to provide excellent answers. When people enjoy reading the site, they are more likely to take some time to write for it.
I took a closer at some of the metrics we use internally to evaluate participation in the site and there seems to be no particular problem. Almost all the high-reputation users are visiting the site on a regular basis. That doesn't mean they always post something, but they are reading and voting. This adds value to the site, though it's not usually something people notice.
There is a core of users who are posting regularly. We'd like to see that core growing. It's not. However, the number of regular posters has held firm for a year or so. There's a substantially larger group who post occasionally. This group has increased noticeably since the start of Ramadan this year. It's still too early to know if these folks will be "hooked" on the site or, having had their questions well-answered, move on.
In any case, there's not much that worrying about it can do.