Mr Sykes said the Ukip win in Clacton was just as important as the party managing to come to within 617 votes of beating Labour in the previously safe northern seat of Heywood and Middleton.
The by-election results have prompted a rethink over just how many marginal seats the party can take, with leader Nigel Farage saying he believed his party could hold the balance of power in 2015.
Mr Sykes, the builder of Sheffield’s Meadowhall shopping centre, put around £1m into this year’s European elections, in which Ukip topped the polls.
Speaking to the Yorkshire Post, he said: “There will be more marginals targeted now than there was before these elections. Rotherham is definitely in our sights, Grimsby is definitely in our sights, but there will be more in the North and elsewhere.
“We will be sitting down and choosing the targets and I will be assisting these targets financially.”
Mr Sykes, whose £650m fortune makes him the 26th wealthiest person in Britain, said that as soon as the result of the upcoming Mark Reckless by-election was known the party would draw up the General Election target list.