This year, I have several new websites (1~2 months old) which used to get good SERP for 1 or 2 weeks , and then dropped suddenly. I found them easy to get good rank with the help of constant blog posts and articles writing. But always the SERP can't last long. And usually before a SERP drop, near all of them had a apparent rank rise ( main search terms get into page 1). According to webmaster tools link report, they all have hundreds or around a thousand of backlinks, and no more than 100 domains. I thought that might be some kind of penalty and stopped link building for these websites. Sometimes I also remove some backlinks and send Google reconsideration, which seems to be helpless. I am always wondering if there is another possibility that Google uses this method to test new websites authority. Google finds a new website get a lot of fresh backlinks and then put it into sandbox. If the website can still get constant and good authority backlinks, the SERP will recover or get even better. Should I give up these websites or just ignore the SERP change and continue to build good backlinks or social signals?