Valli

first of all, never mind if u r an introvert/extrovert.....  

when u hangout with ur chuddy-buddy frnds, u'll be very talkative.....  AND u can express everything clearly in a language u're very familiar with.... if this happens, then u r not an introvert...

but when it comes to presenting urself infront of a crowd, u feel nervous and empty minded..... 

make urself clear if u feel nervous ?? or empty minded ???

if u cant even speak in mother tongue, then thats stage fear..... and thats very easily overcome.....

be clear if u r having stage fear ?? or if u run out of words ??

or if u feel nervous jst bcz u run out of words / not being confident ??

people run out of words especially when they r speaking in a language otherthan their mother tongue

if u run out of words or u if take time to express something in english, then ur problem is sorted.....

when u r about to speak:

u try to think in ur mother tongue , then translate to english and then speak it out

things to do if u r at that stage:

1. listen to somene speaking in english (be it news channels/ movies/ web series.....  of ur interest)

and identify the actions and then make a list of words associated with that action

2. overcome fear to speak in english

3. whatever u see/listen to, try to narrate it in english.

NOTE: revise the keywords u listed before u go to bed

4.now, repeat the step 1 to analyse ur mistakes and identify how words are arranged to make a sentence.

pls dnt under-estimate urself , it takes time to learn something new.... 

5. have patience and repeat the above steps daily

6. think only in english when u r abt to speak (the most imp. one) when u run out of words - ( practice daily)

7. communicate in english ( if u can ) or atleast try to communicate in english after a week of practice or so....

Remember, when u r a child, u had learnt ur mother tongue through observation and practice

i.e.,  by observing how to pronounce , gathering keyterms associated with actions and then trying to speak.

when u r learning any NEW language,  its more like  " listen : speak :: copy : paste " (analogy)

kids dont have fear thats y they r ALWAYS successful in learning any of their mother tongue languages

when u r a kid, u unknowingly implemented the above mentioned analogy and learnt ur mother tongue

do the same thing now to learn english as well

so, overcome fear frst..... start 'listening and then speaking' in english..... have some confidence.... and patience too.... 

if u r very confident , not even ur fears can stop u from presenting urself infront of a crowd.....

7.repeat the step 1 daily to improve vocab. ( u can also read novels of ur intrst )

may be in a month.... u wil be finding urself presenting better than that of before.....

ALL THE BEST ....!!!