After it was reported yesterday that Google has been considering a bid to acquire Twitter the social media company's shares spiked by 4.8 percent - adding over $1.5bn to its value.

The unconfirmed reports came from financial news website Briefing.com - it reported that Twitter has hired Goldman Sachs to fend off two possible takeover attempts - and that Google is one of the interested companies.

When the markets closed yesterday the stock was up by 3.99 percent.

Since the middle of last year there has been a growing feeling that Twitter may have passed its peak - its user growth figures and crucial engagement stats have been waning.

Instagram has overtaken it in both user numbers, and key engagement metrics and a new breed of mobile-focused social apps like Snapchat are offering a new challenge to established social brands.

Google is also under pressure to keep up with Facebook as it challenges it for user attention, and ad revenue.

Twitter would be a nice addition to Google's suite - but it would be an expensive one. The social platform is currently valued at close to $35bn - it's 288m users send over 500m tweets everyday - and 80 percent of its audience use mobile devices.

If a potential deal was to happen it is likely that Google would end up paying closer to $50bn.

Since it was launched in 2006, Twitter has had more than its fair-share of takeover interest. Previous rumours linking Google with the company in January of this year already led to a 3.3 percent rise in Twitter's share price.

In February 2011 it was also reported that Google and Facebook were among a group of firms who approached Twitter with offers close to $10bn.

In 2009 it was rumoured that Google reached advanced negotiations to acquire Twitter for $250m but the deal never materialised.