Many criticised the "senseless violence", making #PrayForLahore one of the top trending topics on Monday.
Some also used #IndiawithPakistan and urged fellow citizens "to stand with Pakistan in this hour of grief".
A Pakistan Taliban group claimed the attack, saying it had targeted Christians celebrating Easter.
The blast hit the main gate of Lahore's Gulshan-e-Iqbal park on Sunday.
The popular park was more crowded than usual, as Lahore's minority Christians were celebrating Easter at a funfair in the premises.
Many Indians, including Bollywood actors Sonakshi Sinha and Sidharth Malhotra, said such attacks "were against humanity".
A similar outpouring of sympathy was seen in India in December 2014 after militants launched an attack on an army school in Peshawar, killing more than 130 children.
Indians on Twitter expressed solidarity with Pakistan after a suicide attack in Lahore killed more than 70 people including children on Sunday.