As far as I know, both means “very”. I would like to know if there are any further differences that exist between them
極 = extremely
很 = very /quite
挻 = quite/ very (colloquial)
甚 = quite/ very
頗 = quite/ considerably
挻 is mostly a colloquial term
We can place all these adverb directly before an adjective
極強 (extremely strong); 很強 (very strong) ; 挻強 (quite strong); 甚強 (quite strong)
we need to add the adjective marker '的' to all these [adverb + adjective] structures before a noun
極強的對手 (extremely strong opponent); 很強的對手 (very strong opponent) ; 挻強的對手 (very strong opponent); 甚強的對手 (very strong opponent)
If the noun is placed before these [adverb + adjective] structures, we don't need the adjective marker '的' (except for 挻)
對手極強 (opponent is extremely strong ); 對手很強 (opponent is very strong ) ; 對手甚強 (opponent is quite strong)
Even the noun is placed before 挻強, we still need to use the adjective marker '的' after it
Example: 對手挻強的 (opponent is quite strong)
We don't usually say 對手挻強
compound words: 極為; 很是; 甚為; 頗為, (挻 doesn't have one)
Yes, both of them are referring to "very". But when you use them, remember there is usually an extra "的" after the "挺" + adjective pair. eg: "挺好的" and "很好" both mean "pretty good, pretty fair"; "他挺好的" and "他很好" are both correct.
Also it seems to me that "很" is stronger than "挺". So "很好" is even better than "挺好的".
＂实用汉语近义虚词 ＂很（副）／颇（副）／挺（副） ［相同］ 都是副词，表示程度比较高，修饰形容词或动词短语。＂很＂口语和书面语都用，＂颇＂用于书面语，＂挺＂多用于口语。句末无语气词＂的＂时，＂很、颇、挺＂有时可以互换：（１）他的话很有道理。（颇✓挺✓）（２）没想到，他对我的这篇论文很感兴趣。（颇✓挺✓）（３）小区离生态公园挺近，交通也很方便。（很✓颇✓）（４）他一个人带着孩子，挺不容易。（很✓颇✓）（５）大家对这件事意见颇多。（很✓挺✓）（６）读了这本书，我颇受启发。（很✓挺✓）［不同］ １。＂挺＂修饰的词语后面可以有＂的＂，＂很、颇＂修饰的词语后面不能有＂的＂：（１）这本书写得挺有意思的，你有空看看吧。（很✗颇✗）（２）瞧这姐妹俩，挺亲热的。（很✗颇✗）（３）老是麻烦你们，挺不好意思的。（很✗颇✗）（４）你这只小手挺脏的，快去洗洗。（很✗颇✗）（５）儿子懂事了，妈妈挺高兴的。（很✗颇✗）（６）马云飞挺重感情，你应该相信他。（很✗颇✗）２。＂很、颇＂可以跟＂有点、有些＂连用，＂挺＂不能：（１）事情闹成这样，张明很有点后悔。（颇✓挺✗）（２）没打好比赛，她心里很有些难过。（颇✓挺✗）
挺 is most used in casual conversations while 很 is used mostly in formal writings.
To me, 很 is more like 'quite', 挺 like 'fairly'. E.g. 很好： quite good; 挺好： fairly good;
'very' would be '非常'. E.g. 非常好： very good.
Compare these three pairs:
你人挺好 -- you are fairly nice.
你人很好 -- you are quite nice.
你人非常好 -- you are very nice.
No doubt I would like to hear most: 你人非常好 -- you are very nice. Compare the first two, I definitely prefer to hear: 你人很好 -- you are quite nice.