Signs point to Thor wielding an axe, likely Jarnbjorn or Stormbreaker.
In the comics, Jarnbjorn is the axe wielded by Thor before he received Mjolnir. Later, when he became unworthy of Mjolnir, he once again picked up Jarnbjorn.
Right now, our best evidence of this comes in two images.
The first is a shot from the first Infinity War trailer.
Thor appears to be attempting to get some sort of large machine moving/activated. The prevailing theory is that it is a star forge used to create the axe.
The second is from a leaked photo of one of the upcoming Lego playsets. The playset is called "The Search For Thor's Weapon", and includes Thor and an unidentified* axe.
*The tweet identifies it as Jarnbjorn, but offers no concrete evidence that it is.
A new leaked image has emerged, purportedly showing a playset version of the hammer called "Stormbreaker". In the comics, Stormbreaker is the axe created for and wielded by Beta Ray Bill (who gets a passing reference/easter egg in Thor Ragnarok).