It is extremely unlikely that a small number of guest post links would poison your backlinks and cause a large ranking drop.

How many guest blog backlinks did you gain? How many total referring links & domains did you already have linking to you?

Recently i got 4 Guest post and all sites are good organic traffics.I have Good backlink profile before 2017 DEC.May be my competitor was generating SPAM ( 7.5K ) link to my site from 7 different domains.I have disavowed all of the domains though in WMT it's still showing.without those SPAM links i have 500+ links from 120+ domains

Are you sure it is just because of these Guest Posts? Even I am suffering from downfall of rankings by the second-half of last week. Though the rankings are not so down but they came down from 1st page to 2nd and some of the keywords went out of 100 directly.

Since you have stated that Guest Posts are NOFOLLOW, they will at least help in driving traffic through your interactive content

Honestly i am not sure about this Drops for Guest POST or What and i have set Link DO FOLLOW.But from Last week i am seeing this Drop

1st one OLD sites and was top( 1,3,2,5) ranking for some high traffics search terms and Lost ranking...

It's not helpful to state you lost rankings. Please state HOW LONG you had those rankings before they dropped. That's important information.

There is more I can say but without that information I can't so I won't.

---

Might not be that it's a guest post. It might be WHERE your guest post is published.

It might not just be WHERE your guest post is published, but it could be that plus on-page factors on your own site.

It could be there was something wrong on your site all the time and that those links only served to confirm the suspicions.

It could be the links had nothing to do with it, that's it was your content all along.

Good luck!
;)

Roger Montti

Have you actually done the normal due care checks to ensure these "guest posts" are not actually built on expired domains that have been through the mills several times and have managed to pick up several layers of penalties on the way?

Unfortunately, many "guest blogs" these days are nothing more than (un)glorified PBNs and really bad ones at that with footprints the size of Eiffel tower. Although Guest Blogging is seen as black/gray hat these days, they rarely cause massive penalties unless abused. What i have seen much more of late is punitive penalties for badly implemented PBNs. I suspect, this is one of those cases.

Unlikely 2 posts will tank a site. Something else is going on. Could be g finally took a deep look (algo wise) at your site and "things changed".

Sites and can go for years without problems and then, bang!, it happens.

No, but they can be the tipping point if there is a host of other issues with the site. Its true though. It could be absolutely anything and it could happen at any time. Google are doing everything in their power to muddy any signs of cause->effect.

Before January i was in 1st Place,Then 21 Jan went 2nd position and Now 3rd Position
Where from i got Guest Post all are getting Organic traffics 5k+ and i did carefully notice before ask Guest Post also variation on Anchor.But Problem is that Got 4 of my guest posts where 2 of them gave link in Content "Conclusion"( END Part) part.It can be a problem ?

Thanks @martinibuster @Shai @tangor

Forgot to mention one more important things.From last November suddenly i saw in WMT that so many SPAM links from SPAM domains,I was updating Disavow file with new SPAM domains.But WMT was not ignoring those links and now it's reach 7K+ link from SPAM domains though i have disavowed all domains where from getting links
I think it can be an Issue ..

Thank You

Before January i was in 1st Place,Then 21 Jan went 2nd position and Now 3rd Position

Unless I am mistaken, you lost a couple positions. Going from 1 to 3 is not a penalty or anything I would honestly be concerned about. Google has patented a method that tricks link spammers into taking moves that will help them confirm a link or links are paid. So if you have them removed, change the anchor text, etc. you risk nullifying any value those links may provide you in the future. If you are getting traffic from these links, it's possible they have a higher bounce rate and that is resulting in a slight decline in ranks. And by all measures it is a slight decline. If I were you I would focus on your users, new content that they may want and less on links.

Getting new links, especially form a few authority sites should cause fluctuation and shuffling.