Colliers International UK chairman Sir John Ritblat has increased his stake in the AIM-quoted property adviser. His non-executive colleague Christopher Newell has also bought shares. Newell, who was a founder of broker Altium, was appointed to the board in 2007 but he did not own any shares before this purchase. Each man bought 650,000 shares at 15p each. This represents an outlay of £97,500 each.Sir John, who is the former chairman of British Land, owns 1.53% of Colliers. This news has pushed up the share price by 2.25p to 17.25p.A rescue fundraising raised £20m at 20p a share just over one year ago. At the same time, FirstService Real Estate Advisors, a subsidiary of Nasdaq-quoted FirstService Corporation took a 29.9% stake. The 20p a share placing price was well below the suspension price of 39.25p a share prior to the announcement of the cash call.Colliers has cut its cost base but it is still losing money. The share price has been drifting lower since the spring and earlier this month it reached 13.75p. Top Director BuysColliers International UK (COL) Director name: Sir John RitblatAmount purchased: 650,000 @ 15.00p Value: £97,500Colliers International UK (COL) Director name: Mr Christopher NewellAmount purchased: 650,000 @ 15.00p Value: £97,500Northern Venture Trust (NVT) Director name: Mr Edward Michael P DennyAmount purchased: 93,898 @ 86.00p Value: £80,752Northern Venture Trust (NVT) Director name: Mr John Randolph HustlerAmount purchased: 63,051 @ 86.00p Value: £54,224Northern Venture Trust (NVT) Director name: Mr Nigel BeerAmount purchased: 49,418 @ 86.00p Value: £42,499Northern Venture Trust (NVT) Director name: Mr Hugh YoungerAmount purchased: 19,535 @ 86.00p Value: £16,800Northern Venture Trust (NVT) Director name: Mr Ross S PetersAmount purchased: 13,971 @ 86.00p Value: £12,015