Hello everyone. Let's say I want to rise my SERP for "I love platypus", and my main domain is www.somethingirrelevant.com. Then I buy the domains iloveplatypus.me, iloveplatypus.us, iloveplatypus.ws, etc and 301 redirect all of them to www.somethingirrelevant.com. Will it help to raise my SERP for "I love platypus" ??
NO! If those 'new' sites (iloveplatypus.me, iloveplatypus.us, iloveplatypus.ws, etc.) that you buy do not have inbound links with "I love platypus", "love", and "platypus" as the link text... simply redirecting the domains with no inbound links will do ABSOLUTELY nothing for your rankings on www.somethingirrelevant.com for the keyword phrase "I love platypus". The domain name being redirected does nothing for your rankings. By 301 redirecting you are passing credit for the inbound links to the old URLs and the link text used on those inbound links to the old URLs to the target of the redirects. Since those domains would not have inbound links it is worthless.
Definitely no, different TLDs will not lead to an increase in SERP for your keyword. Concentrated more on on-site and off-site optimization.
You should avoid excessive 301 redirects from other domains. In past directory owners have been penalized for using this tactics.